Revenue from Contracts with Customers (Impact of ASU 2014-09 on Balance Sheet and Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance premiums and service revenue earned	$ 258	$ 252	$ 753	$ 720
Other revenue	398	381	1,116	1,165
Net revenue	1,505	1,462	4,366	4,292
Compensation and benefits expense	274	264	872	814
Other operating expenses	456	424	1,347	1,249
Noninterest expense	807	753	2,460	2,341
Income from continuing operations before income tax expense	465	395	1,254	1,097
Income tax expense from continuing operations	91	115	280	350
Net income from continuing operations	374	280	974	747
Net income	374	282	973	748
Comprehensive income	241	330	442	892
Premiums receivable and other insurance assets	2,291		2,291			$ 2,047
Other assets	5,796		5,796			5,663
Assets	173,101	164,013	173,101	164,013		167,148
Unearned insurance premiums and service revenue	3,020		3,020			2,604
Liabilities	160,016		160,016			153,654
Accumulated deficit	(5,716)		(5,716)			(6,406)
Equity	13,085	13,573	13,085	13,573	$ 13,375	13,494	$ 13,317
Liabilities and equity	173,101		173,101			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	(8)		(23)
Other revenue	(8)		(23)
Net revenue	(8)		(23)
Compensation and benefits expense	0		(2)
Other operating expenses	(4)		(9)
Noninterest expense	(4)		(11)
Income from continuing operations before income tax expense	(4)		(12)
Income tax expense from continuing operations	(1)		(3)
Net income from continuing operations	(3)		(9)
Net income	(3)		(9)
Comprehensive income	(3)		(9)
Premiums receivable and other insurance assets	133		133
Other assets	44		44
Assets	177		177
Unearned insurance premiums and service revenue	312		312
Liabilities	312		312
Accumulated deficit	(135)		(135)
Equity	(135)		(135)
Liabilities and equity	177		177
Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net income	374	282	973	748
Equity	$ (5,716)	$ (6,533)	$ (5,716)	$ (6,533)	$ (6,510)	$ (6,406)	$ (7,151)