Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Assets
Investment securities – available for sale	$ 96,799	$ 87,358
Mortgage servicing rights	1,680	1,242
Financial derivatives	3,296	4,379
Liabilities
Financial derivatives	$ 824	$ 584
Assets At Fair Value \| Assets, Total
Liabilities
Concentration risk, percentage	23.00%	22.00%
Level 3 Assets \| Assets, Total
Liabilities
Concentration risk, percentage	5.00%	5.00%
Level 3 Assets \| Assets
Liabilities
Concentration risk, percentage	1.00%	1.00%
Liabilities At Fair Value \| Liabilities, Total
Liabilities
Concentration risk, percentage	1.00%	1.00%
Level Three Liabilities \| Liabilities, Total
Liabilities
Concentration risk, percentage	8.00%	9.00%
Level Three Liabilities \| Liability
Liabilities
Concentration risk, percentage	1.00%	1.00%
Fair Value, Recurring
Assets
Investment securities – available for sale	$ 96,799	$ 87,358
Loans	1,441	1,365
Equity investments	2,725	2,629
Trading securities	1,588	2,238
Financial derivatives	4,916	6,533
Other assets	477	454
Total Assets	111,263	103,035
Liabilities
Other borrowed funds	838	707
Financial derivatives	3,023	2,756
Other liabilities	73	43
Total liabilities	3,934	3,506
Level 1 \| Fair Value, Recurring
Assets
Investment securities – available for sale	21,997	16,675
Equity investments	1,133	1,070
Trading securities	576	548
Other assets	384	373
Total Assets	24,090	18,666
Liabilities
Other borrowed funds	790	661
Total liabilities	790	661
Level 2 \| Fair Value, Recurring
Assets
Investment securities – available for sale	73,209	69,036
Loans	730	718
Trading securities	1,012	1,690
Financial derivatives	4,853	6,415
Other assets	93	81
Total Assets	81,313	78,936
Liabilities
Other borrowed funds	46	44
Financial derivatives	2,796	2,483
Total liabilities	2,842	2,527
Level 3 \| Fair Value, Recurring
Assets
Investment securities – available for sale	1,593	1,647
Loans	711	647
Equity investments	1,343	1,263
Financial derivatives	63	118
Total Assets	5,611	5,137
Liabilities
Other borrowed funds	2	2
Financial derivatives	227	273
Other liabilities	73	43
Total liabilities	302	318
Residential mortgage loans held for sale \| Fair Value, Recurring
Assets
Loans held for sale	1,252	854
Residential mortgage loans held for sale \| Level 2 \| Fair Value, Recurring
Assets
Loans held for sale	1,087	691
Residential mortgage loans held for sale \| Level 3 \| Fair Value, Recurring
Assets
Loans held for sale	165	163
Commercial mortgage loans held for sale \| Fair Value, Recurring
Assets
Loans held for sale	385	362
Commercial mortgage loans held for sale \| Level 2 \| Fair Value, Recurring
Assets
Loans held for sale	329	305
Commercial mortgage loans held for sale \| Level 3 \| Fair Value, Recurring
Assets
Loans held for sale	56	57
U.S. Treasury and government agencies \| Fair Value, Recurring
Assets
Investment securities – available for sale	25,950	20,711
U.S. Treasury and government agencies \| Level 1 \| Fair Value, Recurring
Assets
Investment securities – available for sale	21,997	16,675
U.S. Treasury and government agencies \| Level 2 \| Fair Value, Recurring
Assets
Investment securities – available for sale	3,953	4,036
Residential mortgage-backed \| Mortgage-backed Securities Agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	51,554	48,911
Residential mortgage-backed \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	1,424	1,501
Residential mortgage-backed \| Level 2 \| Mortgage-backed Securities Agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	51,554	48,911
Residential mortgage-backed \| Level 2 \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	108	136
Residential mortgage-backed \| Level 3 \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	1,316	1,365
Commercial mortgage-backed \| Mortgage-backed Securities Agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	2,284	2,688
Commercial mortgage-backed \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	4,236	3,689
Commercial mortgage-backed \| Level 2 \| Mortgage-backed Securities Agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	2,284	2,688
Commercial mortgage-backed \| Level 2 \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	4,225	3,678
Commercial mortgage-backed \| Level 3 \| Mortgage-backed Securities Non-agency \| Fair Value, Recurring
Assets
Investment securities – available for sale	11	11
Asset-backed \| Fair Value, Recurring
Assets
Investment securities – available for sale	6,041	5,150
Asset-backed \| Level 2 \| Fair Value, Recurring
Assets
Investment securities – available for sale	5,847	4,951
Asset-backed \| Level 3 \| Fair Value, Recurring
Assets
Investment securities – available for sale	194	199
Other \| Fair Value, Recurring
Assets
Investment securities – available for sale	5,310	4,708
Other \| Level 2 \| Fair Value, Recurring
Assets
Investment securities – available for sale	5,238	4,636
Other \| Level 3 \| Fair Value, Recurring
Assets
Investment securities – available for sale	72	72
Residential mortgage servicing rights \| Fair Value, Recurring
Assets
Mortgage servicing rights	979	673
Residential mortgage servicing rights \| Level 3 \| Fair Value, Recurring
Assets
Mortgage servicing rights	979	673
Commercial mortgage servicing rights \| Fair Value, Recurring
Assets
Mortgage servicing rights	701	569
Commercial mortgage servicing rights \| Level 3 \| Fair Value, Recurring
Assets
Mortgage servicing rights	$ 701	$ 569

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