Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Jun. 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	$ 135	$ 156
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	129	176
Fair Value Option Aggregate Difference Assets	6	(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	697	495
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	674	478
Fair Value Option Aggregate Difference Assets	23	17
Residential Mortgage [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	755	782
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	885	919
Fair Value Option Aggregate Difference Assets	(130)	(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	690	489
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	666	472
Fair Value Option Aggregate Difference Assets	24	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	307	279
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	324	298
Fair Value Option Aggregate Difference Assets	(17)	(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	2	2
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	2	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	275	321
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	284	329
Fair Value Option Aggregate Difference Assets	(9)	(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	5	4
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	6	4
Fair Value Option Aggregate Difference Assets	(1)
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	173	182
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	277	292
Fair Value Option Aggregate Difference Assets	(104)	(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	398	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	411	411
Fair Value Option Aggregate Difference Assets	(13)	(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	397	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	409	411
Fair Value Option Aggregate Difference Assets	(12)	(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)