Parent Company Financial Statements - Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Total revenue	$ 11,170	$ 10,207	$ 10,360
Other expenses	589	584	1,018
Total expenses	8,269	8,077	8,050
Income tax expense (benefit)	722	(22)	318
Net income	2,177	2,143	1,980
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash dividends from consolidated banking subsidiary	2,224	640	585
Cash dividends from consolidated non-banking subsidiaries and unconsolidated entities	12	75	171
Other, net	127	92	73
Total revenue	2,363	807	829
Interest expense	297	249	209
Other expenses	94	107	310
Total expenses	391	356	519
Income tax expense (benefit)	(86)	(47)	(186)
Income before equity in undistributed income of consolidated subsidiaries and unconsolidated entities	2,058	498	496
Consolidated banking subsidiary	20	1,629	1,384
Consolidated non-banking subsidiaries and unconsolidated entities	99	16	100
Net income	$ 2,177	$ 2,143	$ 1,980