Asset Quality (Credit Card and Other Consumer Loan Classes Asset Quality Indicators) (Details) $ in Millions	Sep. 30, 2019 USD ($)		Dec. 31, 2018 USD ($)		Sep. 30, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 237,377	[1]	$ 226,245	[1]	$ 223,053
Automobile Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	16,004		14,419
Automobile Loan [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 16,004		$ 14,419
Weighted average updated FICO score	724		726
Automobile Loan [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 8,444		$ 7,740
Automobile Loan [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,845		4,365
Automobile Loan [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,152		1,007
Automobile Loan [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,240		1,027
Automobile Loan [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	323		280
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,815		6,357
Credit Card [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 6,815		$ 6,357
Weighted average updated FICO score	731		733
Credit Card [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 3,989		$ 3,809
Credit Card [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,955		1,759
Credit Card [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	325		280
Credit Card [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	376		332
Credit Card [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	170		177
Education [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,461		3,822
Education [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,455		$ 1,541
Weighted average updated FICO score	775		774
Education [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,184		$ 1,240
Education [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	185		194
Education [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	22		26
Education [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	22		24
Education [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	42		57
Education [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,006		2,281
Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,856		4,585
Other Consumer [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 2,463		$ 2,157
Weighted average updated FICO score	731		732
Other Consumer [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,452		$ 1,280
Other Consumer [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	755		641
Other Consumer [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	122		106
Other Consumer [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	107		105
Other Consumer [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	27		25
Other Consumer [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 2,393		$ 2,428

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $1.5 billion, Loans of $.8 billion and Other assets of $.1 billion at September 30, 2019 and Loans held for sale of $.9 billion, Loans of $.8 billion and Other assets of $.2 billion at December 31, 2018.