Revenue from Contracts with Customers (Impact of ASU 2014-09 on Balance Sheet and Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018	Dec. 31, 2015
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance premiums and service revenue earned									$ 1,022	$ 973	$ 945
Other revenue	$ 298	$ 398	$ 364	$ 354	$ 379	$ 381	$ 388	$ 396	1,414	1,544	1,530
Net revenue									5,804	5,765	5,437
Compensation and benefits expense									1,155	1,095	992
Other operating expenses									1,814	1,683	1,605
Noninterest expense	804	807	839	814	769	753	810	778	3,264	3,110	2,939
Income from continuing operations before income tax expense	368	465	461	328	410	395	376	326	1,622	1,507	1,581
Income tax expense from continuing operations	79	91	113	76	231	115	122	113	359	581	470
Net income from continuing operations	289	374	348	252	179	280	254	213	1,263	926	1,111
Net income	290	$ 374	$ 349	$ 250	181	$ 282	$ 252	$ 214	1,263	929	1,067
Comprehensive income									974	1,035	957
Premiums receivable and other insurance assets	2,326				2,047				2,326	2,047
Other assets	6,153				5,663				6,153	5,663
Assets	178,869				167,148				178,869	167,148	163,728
Unearned insurance premiums and service revenue	3,044				2,604				3,044	2,604
Liabilities	165,601				153,654				165,601	153,654
Accumulated deficit	(5,489)				(6,406)				(5,489)	(6,406)
Equity	13,268				13,494				13,268	13,494	$ 13,317	$ 13,375	$ 13,439
Liabilities and equity	178,869				$ 167,148				178,869	$ 167,148
Effect of adopting the amendments to Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance premiums and service revenue earned									(26)
Other revenue									(26)
Net revenue									(26)
Compensation and benefits expense									(1)
Other operating expenses									(12)
Noninterest expense									(13)
Income from continuing operations before income tax expense									(13)
Income tax expense from continuing operations									(3)
Net income from continuing operations									(10)
Net income									(10)
Comprehensive income									(10)
Premiums receivable and other insurance assets	135								135
Other assets	44								44
Assets	179								179
Unearned insurance premiums and service revenue	315								315
Liabilities	315								315
Accumulated deficit	(136)								(136)
Equity	(136)								(136)
Liabilities and equity	$ 179								$ 179