Fair Value (Schedule of Assets and Liabilities Measured at Fair Value by Class on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
ASSETS
Investment securities, available-for-sale	$ 20,461	$ 15,731
Trading account	305	266
Total assets	21,836	17,163
LIABILITIES
Securities sold, not yet purchased	32	61
Total liabilities	77	99
U.S. Treasury, agencies and corporations
ASSETS
Investment securities, available-for-sale	18,830	14,136
Municipal securities
ASSETS
Investment securities, available-for-sale	1,556	1,420
Other debt securities
ASSETS
Investment securities, available-for-sale	75	175
Bank-owned life insurance
ASSETS
Other noninterest-bearing investments	535	532
Private equity investments
ASSETS
Other noninterest-bearing investments	122	80
Agriculture loan servicing and interest-only strips
ASSETS
Other assets	14	16
Derivatives | Derivatives designated as hedges
ASSETS
Other assets	10	3
Interest rate | Derivatives not designated as hedging instruments
ASSETS
Other assets	248	411
LIABILITIES
Other liabilities	41	34
Foreign exchange | Derivatives not designated as hedging instruments
ASSETS
Other assets	4	4
LIABILITIES
Other liabilities	4	4
Level 1
ASSETS
Investment securities, available-for-sale	128	192
Trading account	66	111
Total assets	385	427
LIABILITIES
Securities sold, not yet purchased	32	61
Total liabilities	36	65
Level 1 | U.S. Treasury, agencies and corporations
ASSETS
Investment securities, available-for-sale	128	192
Level 1 | Private equity investments
ASSETS
Other noninterest-bearing investments	50
Level 1 | Foreign exchange | Derivatives not designated as hedging instruments
ASSETS
Other assets	4	4
LIABILITIES
Other liabilities	4	4
Level 2
ASSETS
Investment securities, available-for-sale	20,333	15,539
Trading account	239	155
Total assets	21,365	16,640
LIABILITIES
Securities sold, not yet purchased	0	0
Total liabilities	41	34
Level 2 | U.S. Treasury, agencies and corporations
ASSETS
Investment securities, available-for-sale	18,702	13,944
Level 2 | Municipal securities
ASSETS
Investment securities, available-for-sale	1,556	1,420
Level 2 | Other debt securities
ASSETS
Investment securities, available-for-sale	75	175
Level 2 | Bank-owned life insurance
ASSETS
Other noninterest-bearing investments	535	532
Level 2 | Derivatives | Derivatives designated as hedges
ASSETS
Other assets	10	3
Level 2 | Interest rate | Derivatives not designated as hedging instruments
ASSETS
Other assets	248	411
LIABILITIES
Other liabilities	41	34
Level 3
ASSETS
Investment securities, available-for-sale	0	0
Total assets	86	96
LIABILITIES
Securities sold, not yet purchased	0	0
Total liabilities	0	0
Level 3 | U.S. Treasury, agencies and corporations
ASSETS
Investment securities, available-for-sale	0	0
Level 3 | Private equity investments
ASSETS
Other noninterest-bearing investments	72	80
Level 3 | Agriculture loan servicing and interest-only strips
ASSETS
Other assets	14	16
Deferred compensation plan assets | Deferred compensation plan assets
ASSETS
Other assets	137	120
Deferred compensation plan assets | Level 1 | Deferred compensation plan assets
ASSETS
Other assets	$ 137	$ 120