Parent Company FInancial Statements Parent Company Financial Statements (Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Other interest income									$ 71		$ 92		$ 60
Other noninterest income									109		96		108
Interest on medium- and long-term debt									197	[1]	144	[1]	76
Salaries and benefits expense									1,020		1,009		961
Occupancy expense									154		152		154
Equipment expense									50		48		45
Restructuring charges									0		53		45
Other noninterest expenses									81		80		84
Benefit for income taxes	$ 82	$ 80	$ 87	$ 85	$ 90	$ 63	$ 54	$ 93	334		300		491
Net Income	269	292	298	339	310	318	281	326	1,198		1,235		743
Less income allocated to participating securities	2	2	1	2	2	2	2	2	7		8		5
Net income attributable to common shares	$ 267	$ 290	$ 297	$ 337	$ 308	$ 316	$ 279	$ 324	1,191		1,227		738
Parent Company
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries									1,229		1,135		915
Other interest income									20		13		3
Intercompany management fee									224		228		136
Other noninterest income									0		0		8
Total income									1,473		1,376		1,062
Interest on medium- and long-term debt									56		29		13
Salaries and benefits expense									143		140		127
Occupancy expense									6		5		5
Equipment expense									1		1		1
Restructuring charges									0		2		6
Other noninterest expenses									72		75		80
Total expenses									278		252		232
Income before benefit for income taxes and equity in undistributed earnings of subsidiaries									1,195		1,124		830
Benefit for income taxes									(9)		(5)		(26)
Income before equity in undistributed earnings of subsidiaries									1,204		1,129		856
Equity in undistributed earnings of subsidiaries, principally banks									(6)		106		(113)
Net Income									1,198		1,235		743
Less income allocated to participating securities									7		8		5
Net income attributable to common shares									$ 1,191		$ 1,227		$ 738

[1] Includes the effects of hedging.