Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Assets Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 85	$ 132
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	118	125
Fair Value Option Aggregate Difference Assets	(33)	7
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of liabilities for which fair value option was elected	48	63
Aggregate Unpaid Principal Balance, Other borrowed funds	49	64
Difference, Other borrowed funds	(1)	(1)
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	927	819
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	884	798
Fair Value Option Aggregate Difference Assets	43	21
Residential Mortgage [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,080	742
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	1,379	865
Fair Value Option Aggregate Difference Assets	(299)	(123)
Residential Mortgage [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	915	813
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	872	792
Fair Value Option Aggregate Difference Assets	43	21
Residential Mortgage [Member] | Performing Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	289	291
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	303	304
Fair Value Option Aggregate Difference Assets	(14)	(13)
Residential Mortgage [Member] | Loans 90 Days Or More Past Due [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	3	2
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	3	2
Residential Mortgage [Member] | Loans 90 Days Or More Past Due [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	262	285
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	275	296
Fair Value Option Aggregate Difference Assets	(13)	(11)
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	9	4
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	9	4
Fair Value Option Aggregate Difference Assets
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	529	166
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	801	265
Fair Value Option Aggregate Difference Assets	(272)	(99)
Commercial Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	538	246
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	522	265
Fair Value Option Aggregate Difference Assets	16	(19)
Commercial Mortgage [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	537	245
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	521	263
Fair Value Option Aggregate Difference Assets	16	(18)
Commercial Mortgage [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1	1
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	1	2
Fair Value Option Aggregate Difference Assets		$ (1)