Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Other Assets Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	$ 128	$ 156
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	121	176
Fair Value Option Aggregate Difference Assets	7	(20)
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of liabilities for which fair value option was elected	54	64
Aggregate Unpaid Principal Balance, Other borrowed funds	55	65
Difference, Other borrowed funds	(1)	(1)
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	785	495
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	764	478
Fair Value Option Aggregate Difference Assets	21	17
Residential Mortgage [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	754	782
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	880	919
Fair Value Option Aggregate Difference Assets	(126)	(137)
Residential Mortgage [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	780	489
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	759	472
Fair Value Option Aggregate Difference Assets	21	17
Residential Mortgage [Member] | Performing Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	318	279
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	333	298
Fair Value Option Aggregate Difference Assets	(15)	(19)
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 Of Assets For Which Fair Value Option Was Elected	1	2
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	1	2
Residential Mortgage [Member] | Loans 90 Days Or More Past Due [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	270	321
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	281	329
Fair Value Option Aggregate Difference Assets	(11)	(8)
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	4	4
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	4	4
Fair Value Option Aggregate Difference Assets
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	166	182
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	266	292
Fair Value Option Aggregate Difference Assets	(100)	(110)
Commercial Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	750	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	753	411
Fair Value Option Aggregate Difference Assets	(3)	(15)
Commercial Mortgage [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	749	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	751	411
Fair Value Option Aggregate Difference Assets	(2)	(15)
Commercial Mortgage [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	1
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	2
Fair Value Option Aggregate Difference Assets	$ (1)