Goodwill, Other Intangibles, and Property and Equipment - Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite Lived Intangible Assets Net [Line Items]
Cost	$ 1,803	$ 1,772
Accumulated amortization	1,312	1,184
Net carrying value	491	588
Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	1,571	1,540
Accumulated amortization	1,226	1,116
Net carrying value	345	424
Customer relationships [Member] | Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	1,280	1,256
Accumulated amortization	1,056	965
Net carrying value	224	291
Other intangibles [Member] | Other assets [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	291	284
Accumulated amortization	170	151
Net carrying value	121	133
Value of business acquired [Member] | Deferred policy acquisition costs [Member]
Finite Lived Intangible Assets Net [Line Items]
Cost	232	232
Accumulated amortization	86	68
Net carrying value	$ 146	$ 164