Goodwill, Other Intangibles, and Property and Equipment - Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Finite Lived Intangible Assets Net [Line Items]
Cost	$ 4,538	$ 4,240
Accumulated amortization	3,181	2,754
Net carrying value	1,357	1,486
Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	1,540	1,566
Accumulated amortization	1,116	998
Net carrying value	424	568
Customer relationships [Member] | Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	1,256	1,264
Accumulated amortization	965	867
Net carrying value	291	397
Other intangibles [Member] | Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	284	302
Accumulated amortization	151	131
Net carrying value	133	171
Value of business acquired [Member] | Deferred policy acquisition costs [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	232	232
Accumulated amortization	68	48
Net carrying value	164	184
Internal-use software [Member] | Property and equipment [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	2,766	2,442
Accumulated amortization	1,997	1,708
Net carrying value	$ 769	$ 734