Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Securities available for sale, fair value	$ 57,618	$ 60,104
Mortgage servicing rights	1,832	1,758
Fair Value, Measurements, Recurring
Assets
Total debt securities	57,033	59,503
Securities available for sale, fair value	57,618	60,104
Loans	869	893
Equity investments	1,265	1,381
Trading Securities	2,915	2,629
Financial derivatives	2,874	4,616
Other assets	638	817
Total Assets	69,673	74,608
Liabilities
Other borrowed funds	1,344	970
Financial derivatives	2,856	3,839
Other Liabilities, Fair Value Disclosure	33	9
Total liabilities	4,233	4,818
Residential Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	832	1,010
Mortgage servicing rights	1,164	1,182
Commercial Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	830	1,400
Mortgage servicing rights	668	576
US Treasury and Government Agencies Securities \| Fair Value, Measurements, Recurring
Assets
Total debt securities	14,521	13,174
Residential mortgage-backed Securities \| Mortgage-backed Securities Agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	25,406	26,128
Residential mortgage-backed Securities \| Mortgage-backed Securities Non-agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	2,758	3,366
Commercial Mortgage Backed Securities \| Mortgage-backed Securities Agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	1,904	2,119
Commercial Mortgage Backed Securities \| Mortgage-backed Securities Non-agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	2,613	4,025
Asset backed \| Fair Value, Measurements, Recurring
Assets
Total debt securities	5,397	5,968
Other Debt Obligations \| Fair Value, Measurements, Recurring
Assets
Total debt securities	4,434	4,723
Other Assets \| Fair Value, Measurements, Recurring
Assets
Securities available for sale, fair value	585	601
Level 1 \| Fair Value, Measurements, Recurring
Assets
Total debt securities	14,088	12,572
Securities available for sale, fair value	14,612	13,113
Trading Securities	1,243	1,458
Financial derivatives		10
Other assets	278	266
Total Assets	16,133	14,847
Liabilities
Other borrowed funds	1,079	799
Financial derivatives		1
Total liabilities	1,079	800
Level 1 \| US Treasury and Government Agencies Securities \| Fair Value, Measurements, Recurring
Assets
Total debt securities	14,088	12,572
Level 1 \| Other Assets \| Fair Value, Measurements, Recurring
Assets
Securities available for sale, fair value	524	541
Level 2 \| Fair Value, Measurements, Recurring
Assets
Total debt securities	39,865	43,208
Securities available for sale, fair value	39,926	43,268
Loans	571	558
Trading Securities	1,670	1,169
Financial derivatives	2,864	4,566
Other assets	253	312
Total Assets	46,836	50,881
Liabilities
Other borrowed funds	254	161
Financial derivatives	2,369	3,424
Total liabilities	2,623	3,585
Level 2 \| Residential Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	829	1,008
Level 2 \| Commercial Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	723
Level 2 \| US Treasury and Government Agencies Securities \| Fair Value, Measurements, Recurring
Assets
Total debt securities	433	602
Level 2 \| Residential mortgage-backed Securities \| Mortgage-backed Securities Agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	25,406	26,128
Level 2 \| Residential mortgage-backed Securities \| Mortgage-backed Securities Non-agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	97	112
Level 2 \| Commercial Mortgage Backed Securities \| Mortgage-backed Securities Agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	1,904	2,119
Level 2 \| Commercial Mortgage Backed Securities \| Mortgage-backed Securities Non-agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	2,613	4,025
Level 2 \| Asset backed \| Fair Value, Measurements, Recurring
Assets
Total debt securities	5,065	5,565
Level 2 \| Other Debt Obligations \| Fair Value, Measurements, Recurring
Assets
Total debt securities	4,347	4,657
Level 2 \| Other Assets \| Fair Value, Measurements, Recurring
Assets
Securities available for sale, fair value	61	60
Level 3 \| Fair Value, Measurements, Recurring
Assets
Total debt securities	3,080	3,723
Securities available for sale, fair value	3,080	3,723
Loans	298	335
Equity investments	1,036	1,331
Trading Securities	2	2
Financial derivatives	10	40
Other assets	107	239
Total Assets	6,475	8,830
Liabilities
Other borrowed funds	11	10
Financial derivatives	487	414
Other Liabilities, Fair Value Disclosure	33	9
Total liabilities	531	433
Level 3 \| Residential Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	3	2
Mortgage servicing rights	1,164	1,182
Level 3 \| Commercial Mortgage \| Fair Value, Measurements, Recurring
Assets
Loans held for sale	107	1,400
Mortgage servicing rights	668	576
Level 3 \| Residential mortgage-backed Securities \| Mortgage-backed Securities Non-agency \| Fair Value, Measurements, Recurring
Assets
Total debt securities	2,661	3,254
Level 3 \| Asset backed \| Fair Value, Measurements, Recurring
Assets
Total debt securities	332	403
Level 3 \| Other Debt Obligations \| Fair Value, Measurements, Recurring
Assets
Total debt securities	$ 87	$ 66

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