Loans - Consumer, Excluding Credit Card Loans, Financial Effects of Modification (Details) (Consumer, excluding credit card, USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 31, 2014
Business banking
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan	1 year
Modifications, subsequent default, recorded investment	$ 25	$ 43	$ 42
Auto
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan	1 year
Modifications, subsequent default, recorded investment	$ 43	$ 54	$ 46
Scored Auto and Business Banking Loans
Financing Receivable, Impaired [Line Items]
Number of payments past due for deemed payment	2
Student Loans
Financing Receivable, Impaired [Line Items]
Deferment Period Extension				24 months