New Accounting Pronouncements (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Liability for off-balance sheet credit exposures	$ 253	$ 371	$ 158	$ 158	$ 90	$ 89	$ 96
Retained earnings	303			1,534
Allowance for credit losses	$ 1,192	$ 931	467	637	$ 613	$ 583	$ 541
Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Liability for off-balance sheet credit exposures			54
Allowance for credit losses			(170)
Commercial Loans [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			(126)
Consumer Loans [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses			(44)
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses				$ 467
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			82
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Student Loan [Member] | Accounting Standards Update 2016-13 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings			$ 2