Acquisitions Intangible Assets (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 14, 2016	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Intangible Assets Acquired	$ 7,655
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Unearned premium reserves [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		1 year
Distribution Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		24 years
The Chubb Corporation [Member] | Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 95
The Chubb Corporation [Member] | Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		2,800
The Chubb Corporation [Member] | Unearned premium reserves [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		1,550
The Chubb Corporation [Member] | Distribution Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		3,150
The Chubb Corporation [Member] | Licensing Agreements [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		50
The Chubb Corporation [Member] | Syndicate capacity [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 10