Parent Company Financial Statements - Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Total revenue	$ 10,360	$ 10,274	$ 9,864
Other expenses	1,018	751	547
Total expenses	8,050	7,827	7,192
Income tax expense	318	415	616
Net income	1,980	2,022	2,050
Parent Company
Condensed Financial Statements, Captions [Line Items]
Cash dividends from consolidated banking subsidiary	585	1,470	1,694
Cash dividends from consolidated non-banking subsidiaries and unconsolidated entities	171	138	250
Other, net	73	63	35
Total revenue	829	1,671	1,979
Interest expense	209	193	169
Other expenses	310	55	88
Total expenses	519	248	257
Income tax expense	(186)	(83)	(84)
Income (loss) before equity in undistributed income of consolidated subsidiaries and unconsolidated entities	496	1,506	1,806
Consolidated banking subsidiary	1,384	360	151
Consolidated non-banking subsidiaries and unconsolidated entities	100	156	93
Net income	$ 1,980	$ 2,022	$ 2,050