Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Assets
Investment securities – available for sale	$ 89,747	$ 69,163
Mortgage servicing rights	1,113	1,644
Financial derivatives	4,780	2,196
Liabilities
Financial derivatives	$ 538	$ 539
Assets At Fair Value [Member] \| Assets, Total [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Concentration risk, percentage	23.00%	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	6.00%	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	$ 89,747	$ 69,163
Loans	1,301	742
Equity investments	2,236	2,421
Trading securities	1,721	3,220
Financial derivatives	7,343	3,502
Other assets	404	470
Total Assets	105,231	82,227
Liabilities
Other borrowed funds	820	518
Financial derivatives	2,710	2,019
Other liabilities	90	137
Total liabilities	3,620	2,674
Level 1 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	17,946	16,236
Equity investments	691	855
Trading securities	660	433
Other assets	344	339
Total Assets	19,641	17,863
Liabilities
Other borrowed funds	777	385
Financial derivatives	2
Total liabilities	779	385
Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	70,073	50,872
Loans	654	442
Trading securities	1,061	2,787
Financial derivatives	7,206	3,448
Other assets	60	131
Total Assets	80,284	58,679
Liabilities
Other borrowed funds	41	126
Financial derivatives	2,565	1,819
Total liabilities	2,606	1,945
Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	1,728	2,055
Loans	647	300
Equity investments	1,259	1,276
Financial derivatives	137	54
Total Assets	5,020	5,395
Liabilities
Other borrowed funds	2	7
Financial derivatives	143	200
Other liabilities	90	137
Total liabilities	235	344
Residential Mortgage [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	660	819
Mortgage servicing rights	598	995
Residential Mortgage [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	583	817
Residential Mortgage [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	77	2
Mortgage servicing rights	598	995
Commercial Mortgage [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	706	246
Mortgage servicing rights	515	649
Commercial Mortgage [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	647	182
Commercial Mortgage [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Loans held for sale	59	64
Mortgage servicing rights	515	649
US Treasury and Government [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	18,225	16,516
US Treasury and Government [Member] \| Level 1 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	17,946	16,236
US Treasury and Government [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	279	280
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	52,928	36,321
Residential Mortgage-backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	1,603	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	52,928	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	165	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	1,438	1,741
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	2,966	3,118
Commercial Mortgage Backed Securities [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	3,829	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	2,966	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	3,818	3,372
Commercial Mortgage Backed Securities [Member] \| Level 3 [Member] \| Mortgage-backed Securities Non-agency [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	11
Asset backed [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,240	5,114
Asset backed [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	5,032	4,874
Asset backed [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	208	240
Other [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	4,956	2,908
Other [Member] \| Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	4,885	2,834
Other [Member] \| Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Investment securities – available for sale	$ 71	$ 74

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