Asset Quality (Automobile, Credit Card, Education and Other Consumer Loan Classes Asset Quality Indicators) (Details) $ in Millions	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 226,245	[1]	$ 220,458	[1]	$ 210,833
Automobile
Financing Receivable, Recorded Investment [Line Items]
Total Loans	14,419		12,880
Automobile | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 14,419		$ 12,833
Weighted average FICO score	726		738
Automobile | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 7,740		$ 7,825
Automobile | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,365		3,636
Automobile | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,007		543
Automobile | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,027		587
Automobile | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	280		242
Automobile | Other Internal Credit Metrics
Financing Receivable, Recorded Investment [Line Items]
Total Loans			47
Credit Card
Financing Receivable, Recorded Investment [Line Items]
Total Loans	6,357		5,699
Credit Card | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 6,357		$ 5,699
Weighted average FICO score	733		735
Credit Card | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 3,809		$ 3,457
Credit Card | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	1,759		1,596
Credit Card | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	280		250
Credit Card | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	332		272
Credit Card | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	177		124
Education
Financing Receivable, Recorded Investment [Line Items]
Total Loans	3,822		4,454
Education | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,541		$ 1,634
Weighted average FICO score	774		773
Education | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,240		$ 1,315
Education | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	194		209
Education | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	26		31
Education | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	24		30
Education | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	57		49
Education | Other Internal Credit Metrics
Financing Receivable, Recorded Investment [Line Items]
Total Loans	2,281		2,820
Other Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	4,585		4,410
Other Consumer | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 2,157		$ 1,939
Weighted average FICO score	732		737
Other Consumer | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,280		$ 1,226
Other Consumer | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	641		507
Other Consumer | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	106		85
Other Consumer | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	105		98
Other Consumer | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	25		23
Other Consumer | Other Internal Credit Metrics
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 2,428		$ 2,471

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $.9 billion, Loans of $.8 billion, and Other assets of $.2 billion at December 31, 2018 and Loans held for sale of $1.7 billion, Loans of $.9 billion, and Other assets of $.3 billion at December 31, 2017.