Asset Quality (Credit Card and Other Consumer Loan Classes Asset Quality Indicators) (Details) $ in Millions	Jun. 30, 2019 USD ($)		Dec. 31, 2018 USD ($)		Jun. 30, 2018 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 237,215	[1]	$ 226,245	[1]	$ 222,855
Automobile Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	15,612		14,419
Automobile Loan [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 15,612		$ 14,419
Weighted average updated FICO score	726		726
Automobile Loan [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 8,358		$ 7,740
Automobile Loan [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,679		4,365
Automobile Loan [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,076		1,007
Automobile Loan [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,163		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	336		280
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,511		6,357
Credit Card [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 6,511		$ 6,357
Weighted average updated FICO score	733		733
Credit Card [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 3,918		$ 3,809
Credit Card [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,846		1,759
Credit Card [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	297		280
Credit Card [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	332		332
Credit Card [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	118		177
Education [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,555		3,822
Education [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,485		$ 1,541
Weighted average updated FICO score	777		774
Education [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,223		$ 1,240
Education [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	176		194
Education [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	23		26
Education [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	23		24
Education [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	40		57
Education [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,070		2,281
Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,710		4,585
Other Consumer [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 2,338		$ 2,157
Weighted average updated FICO score	732		732
Other Consumer [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,393		$ 1,280
Other Consumer [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	705		641
Other Consumer [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	111		106
Other Consumer [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	102		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	$ 2,372		$ 2,428

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $1.1 billion, Loans of $.8 billion and Other assets of $.1 billion at June 30, 2019 and Loans held for sale of $.9 billion, Loans of $.8 billion and Other assets of $.2 billion at December 31, 2018.