Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Assets
Investment securities – available for sale	$ 42,280	$ 41,785
Mortgage servicing rights	3,762	3,686
Financial derivatives	743	897
Liabilities
Financial derivatives	3,922	3,538
Other liabilities, fair value	$ 100	$ 100
Assets At Fair Value | Assets, Total | Assets
Liabilities
Concentration risk, percentage	10.00%	10.00%
Level 3 Assets | Assets, Total | Assets
Liabilities
Concentration risk, percentage	13.00%	13.00%
Level 3 Assets | Assets | Assets
Liabilities
Concentration risk, percentage	1.00%	1.00%
Liabilities At Fair Value | Liabilities, Total | Liability
Liabilities
Concentration risk, percentage	1.00%	1.00%
Level Three Liabilities | Liabilities, Total | Liability
Liabilities
Concentration risk, percentage	4.00%	6.00%
Level Three Liabilities | Liability | Liability
Liabilities
Concentration risk, percentage	1.00%	1.00%
Fair Value, Recurring
Assets
Investment securities – available for sale	$ 42,280	$ 41,785
Loans	1,217	1,238
Equity investments	2,739	2,717
Trading securities	2,466	2,799
Financial derivatives	3,332	3,429
Other assets	533	496
Total Assets	57,050	56,862
Liabilities
Other borrowed funds	979	817
Financial derivatives	6,365	5,899
Other liabilities, fair value	189	237
Total liabilities	7,533	6,953
Level 1 | Fair Value, Recurring
Assets
Investment securities – available for sale	6,962	6,292
Equity investments	511	574
Trading securities	468	377
Financial derivatives	12	29
Other assets	425	403
Total Assets	8,378	7,675
Liabilities
Other borrowed funds	861	724
Financial derivatives	9	11
Total liabilities	870	735
Level 2 | Fair Value, Recurring
Assets
Investment securities – available for sale	34,394	34,537
Loans	504	512
Trading securities	1,998	2,422
Financial derivatives	3,311	3,394
Other assets	100	85
Total Assets	40,919	41,548
Liabilities
Other borrowed funds	109	84
Financial derivatives	6,243	5,736
Total liabilities	6,352	5,820
Level 3 | Fair Value, Recurring
Assets
Investment securities – available for sale	924	956
Loans	713	726
Equity investments	2,030	1,952
Financial derivatives	9	6
Other assets	8	8
Total Assets	7,555	7,448
Liabilities
Other borrowed funds	9	9
Financial derivatives	113	152
Other liabilities, fair value	189	237
Total liabilities	311	398
Residential mortgage loans held for sale | Fair Value, Recurring
Assets
Loans held for sale	520	474
Residential mortgage loans held for sale | Level 2 | Fair Value, Recurring
Assets
Loans held for sale	422	371
Residential mortgage loans held for sale | Level 3 | Fair Value, Recurring
Assets
Loans held for sale	98	103
Commercial mortgage loans held for sale | Fair Value, Recurring
Assets
Loans held for sale	201	238
Commercial mortgage loans held for sale | Level 2 | Fair Value, Recurring
Assets
Loans held for sale	190	227
Commercial mortgage loans held for sale | Level 3 | Fair Value, Recurring
Assets
Loans held for sale	11	11
U.S. Treasury and government agencies | Fair Value, Recurring
Assets
Investment securities – available for sale	7,880	6,951
U.S. Treasury and government agencies | Level 1 | Fair Value, Recurring
Assets
Investment securities – available for sale	6,962	6,292
U.S. Treasury and government agencies | Level 2 | Fair Value, Recurring
Assets
Investment securities – available for sale	918	659
Residential mortgage-backed | Mortgage-backed Securities Agency | Fair Value, Recurring
Assets
Investment securities – available for sale	26,842	27,880
Residential mortgage-backed | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale	668	696
Residential mortgage-backed | Level 2 | Mortgage-backed Securities Agency | Fair Value, Recurring
Assets
Investment securities – available for sale	26,842	27,880
Residential mortgage-backed | Level 2 | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale
Residential mortgage-backed | Level 3 | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale	668	696
Commercial mortgage servicing rights | Mortgage-backed Securities Agency | Fair Value, Recurring
Assets
Investment securities – available for sale	1,639	1,546
Commercial mortgage servicing rights | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale	834	869
Commercial mortgage servicing rights | Level 2 | Mortgage-backed Securities Agency | Fair Value, Recurring
Assets
Investment securities – available for sale	1,639	1,546
Commercial mortgage servicing rights | Level 2 | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale	731	766
Commercial mortgage servicing rights | Level 3 | Mortgage-backed Securities Non-agency | Fair Value, Recurring
Assets
Investment securities – available for sale	103	103
Asset-backed | Fair Value, Recurring
Assets
Investment securities – available for sale	1,827	1,116
Asset-backed | Level 2 | Fair Value, Recurring
Assets
Investment securities – available for sale	1,727	1,014
Asset-backed | Level 3 | Fair Value, Recurring
Assets
Investment securities – available for sale	100	102
Other | Fair Value, Recurring
Assets
Investment securities – available for sale	2,590	2,727
Other | Level 2 | Fair Value, Recurring
Assets
Investment securities – available for sale	2,537	2,672
Other | Level 3 | Fair Value, Recurring
Assets
Investment securities – available for sale	53	55
Residential mortgage servicing rights | Fair Value, Recurring
Assets
Mortgage servicing rights	2,687	2,654
Residential mortgage servicing rights | Level 3 | Fair Value, Recurring
Assets
Mortgage servicing rights	2,687	2,654
Commercial mortgage servicing rights | Fair Value, Recurring
Assets
Mortgage servicing rights	1,075	1,032
Commercial mortgage servicing rights | Level 3 | Fair Value, Recurring
Assets
Mortgage servicing rights	$ 1,075	$ 1,032