Asset Quality (Credit Card and Other Consumer Loan Classes Asset Quality Indicators) (Details) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017		Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 223,053	[1]	$ 220,458	[1]	$ 221,109
% of Loans	100.00%		100.00%
Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,979		$ 5,699
Credit Card [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,979		$ 5,699
% of Loans	100.00%		100.00%
Weighted average updated FICO score	732		735
Credit Card [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 3,588		$ 3,457
% of Loans	60.00%		61.00%
Credit Card [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,672		$ 1,596
% of Loans	28.00%		28.00%
Credit Card [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 268		$ 250
% of Loans	5.00%		4.00%
Credit Card [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 326		$ 272
% of Loans	5.00%		5.00%
Credit Card [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 125		$ 124
% of Loans	2.00%		2.00%
Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 22,795		$ 21,744
Other Consumer [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 17,949		$ 16,406
% of Loans	100.00%		100.00%
Weighted average updated FICO score	733		741
Other Consumer [Member] | FICO Score - Greater than 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 10,385		$ 10,366
% of Loans	58.00%		63.00%
Other Consumer [Member] | FICO Score - 650 to 719 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,087		$ 4,352
% of Loans	28.00%		27.00%
Other Consumer [Member] | FICO Score - 620 to 649 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,048		$ 659
% of Loans	6.00%		4.00%
Other Consumer [Member] | FICO Score - Less than 620 [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,034		$ 715
% of Loans	6.00%		4.00%
Other Consumer [Member] | No FICO Score Available Or Required [Member] | Using FICO Credit Metric [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 395		$ 314
% of Loans	2.00%		2.00%
Other Consumer [Member] | Other Internal Credit Metrics [Member]
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 4,846		$ 5,338

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $1.0 billion, Loans of $.8 billion and Other assets of $.2 billion at September 30, 2018 and Loans held for sale of $1.7 billion, Loans of $.9 billion and Other assets of $.3 billion at December 31, 2017.