Goodwill and other intangible assets Schedule of finite-lived intangible assets acquired (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 14, 2016	Mar. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Total identified intangible assets acquired	$ 7,655
Unearned premium reserves [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 1,550
Estimated Useful Life		1 year
Agency distribution relationships and renewal rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 3,150
Estimated Useful Life		24 years
Internally Developed Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 95
Estimated Useful Life		3 years
Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 2,800
Syndicate capacity [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		10
Licenses [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 50