Intangible Assets Intanibgle Assets (Schedule of intangible assets acquired in connection with Chubb Corp)(Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 14, 2016	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Total identified intangible assets	$ 7,655
Trademarks [Member] | The Chubb Corporation [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 2,800
Licensing Agreements [Member] | The Chubb Corporation [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		50
Syndicate capacity [Member] | The Chubb Corporation [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets Acquired		$ 10
Unearned premium reserves [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		1 year
Unearned premium reserves [Member] | The Chubb Corporation [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 1,550
Agency distribution relationships and renewal rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		24 years
Agency distribution relationships and renewal rights [Member] | The Chubb Corporation [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 3,150
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Developed Technology Rights [Member] | The Chubb Corporation [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired		$ 95