Parent Company FInancial Statements Parent Company Financial Statements (Statements of Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Other interest income									$ 14	$ 14	$ 12
Other noninterest income									142	168	158
Interest on medium- and long-term debt									50	57	65
Salaries and benefits expense									980	1,009	1,018
Net occupancy expense									171	160	163
Equipment expense									57	60	65
Merger and restructuring charges									0	0	35
Other noninterest expenses									173	179	191
Benefit for income taxes	70	73	70	64	50	68	64	63	277	245	241
Net income	149	154	151	139	117	147	143	134	593	541	521
Less income allocated to participating securities	1	2	2	2	2	2	2	2	7	8	6
Net income attributable to common shares	148	152	149	137	115	145	141	132	586	533	515
Parent Company
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries									384	490	505
Other interest income									1	1	1
Intercompany management fees									118	110	108
Other noninterest income									7	14	7
Total income									510	615	621
Interest on medium- and long-term debt									14	11	11
Salaries and benefits expense									114	118	114
Net occupancy expense									5	4	7
Equipment expense									1	1	1
Merger and restructuring charges									0	0	35
Other noninterest expenses									70	78	54
Total expenses									204	212	222
Income before benefit for income taxes and equity in undistributed earnings of subsidiaries									306	403	399
Benefit for income taxes									(27)	(30)	(37)
Income before equity in undistributed earnings of subsidiaries									333	433	436
Equity in undistributed earnings of subsidiaries, principally banks									260	108	85
Net income									593	541	521
Less income allocated to participating securities									7	8	6
Net income attributable to common shares									$ 586	$ 533	$ 515