He donated at least US$263 million to New York cultural, civic and philanthropic causes. Some recipients were typical targets for the wealthy - he has given the Metropolitan Museum of Art US$30 million to pay for audio guides and wireless internet. But he also gave a similar sum to underwrite projects helping disadvantaged young black and Latino men in low-income districts.
Bloomberg effectively gave the city US$2.7 million by taking only US$1 of the annual US$225,000 salary. He funded all staff travel by private jet on his frequent jaunts, at a total cost of about US$6 million.
He also paid for a light breakfast and lunch - healthy eating is one of his many causes - for his aides each day out of his own pocket. And he installed two giant aquariums for his beloved tropical fish at City Hall, financing their maintenance and cleaning each week (estimated cost: US$62,400).
It is unlikely that his successor, Bill de Blasio, a career Democrat politician, will even attempt to rival such extravagances.
Nor were Bloomberg's outgoings limited to the boundaries of the city's five boroughs. He has spent at least US$20 million across the US to promote issues such as gun control, immigration reform and climate change.
The mayor's free-spending ways are also being felt in London, where he is expected to spend much of his time. Bloomberg will be the next chairman of the Serpentine Gallery after an undisclosed donation helped to pay for an extension. He has overseen renovations at his US$20 million home in Cadogan Square, Knightsbridge, and is also paying for the construction of grandiose London headquarters for his business.
In political terms, his aides tout the virtues of his financial independence. Bloomberg's near-bottomless coffers certainly mean that he is free from the demands of party voters and donors. Indeed, he flipped from lifelong Democrat to Republican to win the nomination to run for mayor in 2001 and then switched to registered independent when he was exploring a self-funded run for President.
In 2009, Bill Thompson, his Democrat rival for mayor, called Bloomberg's spending "obscene" after he was outspent by a factor of 14 times. But despite his financial dominance, Bloomberg won just 50.7 per cent of the vote, suggesting his expenditure had turned off many New Yorkers. Mark Green, whom he defeated in his first campaign in 2001, described him as "a modern Medici", a reference to the medieval Italian political dynasty, banking family and later royal house.
Chris McNickle, a historian of city politics, said Bloomberg's fortune had made him New York's most influential mayor. "He has used his wealth to intensify and extend his power and shape New York according to his dream for the city.
"He has overwhelmingly done good things for the city, but his spending raises basic questions about democratic principles and practice."
Bloomberg leaves City Hall with a number of impressive records to his name - violent crime is at unprecedented lows, tourism at an all-time high - and a raft of initiatives on public health and the environment.
But even by the standards of a country where money is king in politics, it is his personal expenditure while in the job that is perhaps most striking.
