Asset Quality (Credit Card and Other Consumer Loan Classes Asset Quality Indicators) (Details) - USD ($) $ in Millions	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 220,458	[1]	$ 210,833	[1]	$ 206,696
% of Loans	100.00%		100.00%
Credit Card
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,699		$ 5,282
Credit Card | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,699		$ 5,282
% of Loans	100.00%		100.00%
Weighted average FICO score	735		736
Credit Card | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 3,457		$ 3,244
% of Loans	61.00%		61.00%
Credit Card | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 1,596		$ 1,466
% of Loans	28.00%		28.00%
Credit Card | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 250		$ 215
% of Loans	4.00%		4.00%
Credit Card | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 272		$ 229
% of Loans	5.00%		4.00%
Credit Card | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 124		$ 128
% of Loans	2.00%		3.00%
Other Consumer
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 21,744		$ 22,049
Other Consumer | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 16,406		$ 15,793
% of Loans	100.00%		100.00%
Weighted average FICO score	741		744
Other Consumer | FICO Score - Greater than 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 10,366		$ 10,247
% of Loans	63.00%		65.00%
Other Consumer | FICO Score - 650 to 719 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 4,352		$ 3,873
% of Loans	27.00%		25.00%
Other Consumer | FICO Score - 620 to 649 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 659		$ 552
% of Loans	4.00%		3.00%
Other Consumer | FICO Score - Less than 620 | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 715		$ 632
% of Loans	4.00%		4.00%
Other Consumer | No FICO Score Available Or Required | Using FICO Credit Metric
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 314		$ 489
% of Loans	2.00%		3.00%
Other Consumer | Other Internal Credit Metrics
Financing Receivable, Recorded Investment [Line Items]
Total Loans	$ 5,338		$ 6,256

[1] Our consolidated assets included the following for which we have elected the fair value option: Loans held for sale of $1.7 billion, Loans of $.9 billion, and Other assets of $.3 billion at December 31, 2017 and Loans held for sale of $2.4 billion, Loans of $.9 billion, and Other assets of $.5 billion at December 31, 2016.