Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Assets
Investment securities – available for sale	$ 89,077	$ 69,163
Mortgage servicing rights	1,082	1,644
Financial derivatives	5,322	2,196
Liabilities
Financial derivatives	$ 1,478	$ 539
Assets At Fair Value [Member] \| Assets, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	24.00%	20.00%
Level Three Assets [Member] \| Assets, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	5.00%	7.00%
Level Three Assets [Member] \| Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	1.00%	1.00%
Liabilities At Fair Value [Member] \| Liabilities, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	1.00%	1.00%
Level Three Liabilities [Member] \| Liabilities, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	5.00%	13.00%
Level Three Liabilities [Member] \| Liability [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	1.00%	1.00%
Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	$ 89,077	$ 69,163
Loans	1,080	742
Equity investments	2,014	2,421
Trading securities	4,017	3,220
Financial derivatives	8,773	3,502
Other assets	371	470
Total Assets	107,879	82,227
Liabilities
Other borrowed funds	1,424	518
Financial derivatives	3,928	2,019
Other liabilities	72	137
Total liabilities	5,424	2,674
Level 1 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	16,699	16,236
Equity investments	500	855
Trading securities	1,976	433
Financial derivatives	3
Other assets	286	339
Total Assets	19,464	17,863
Liabilities
Other borrowed funds	1,363	385
Financial derivatives	3
Total liabilities	1,366	385
Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	70,661	50,872
Loans	425	442
Trading securities	2,041	2,787
Financial derivatives	8,635	3,448
Other assets	85	131
Total Assets	83,248	58,679
Liabilities
Other borrowed funds	56	126
Financial derivatives	3,740	1,819
Total liabilities	3,796	1,945
Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	1,717	2,055
Loans	655	300
Equity investments	1,220	1,276
Financial derivatives	135	54
Total Assets	4,873	5,395
Liabilities
Other borrowed funds	5	7
Financial derivatives	185	200
Other liabilities	72	137
Total liabilities	262	344
Residential Mortgage [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	927	819
Mortgage servicing rights	605	995
Residential Mortgage [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	923	817
Residential Mortgage [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	4	2
Mortgage servicing rights	605	995
Commercial Mortgage [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	538	246
Mortgage servicing rights	477	649
Commercial Mortgage [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	478	182
Commercial Mortgage [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	60	64
Mortgage servicing rights	477	649
US Treasury and Government [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	16,981	16,516
US Treasury and Government [Member] \| Level 1 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	16,699	16,236
US Treasury and Government [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	282	280
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	52,628	36,321
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	1,643	1,814
Residential Mortgage-backed Securities [Member] \| Level 2 [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	52,628	36,321
Residential Mortgage-backed Securities [Member] \| Level 2 [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	201	73
Residential Mortgage-backed Securities [Member] \| Level 3 [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	1,442	1,741
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	3,289	3,118
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	4,082	3,372
Commercial Mortgage Backed Securities [Member] \| Level 2 [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	3,289	3,118
Commercial Mortgage Backed Securities [Member] \| Level 2 [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	4,082	3,372
Asset backed [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,278	5,114
Asset backed [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,076	4,874
Asset backed [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	202	240
Other [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,176	2,908
Other [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,103	2,834
Other [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	$ 73	$ 74

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