Loans - Consumer Banking: Net Charge-Offs (Detail) (Consumer Banking, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 675	$ 616
Percentage annualized net charge-off by average loans held for investment	0.95%	0.85%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)	1.49%	1.51%
Auto
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	619	546
Percentage annualized net charge-off by average loans held for investment	1.78%	1.85%
Home loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	17	16
Percentage annualized net charge-off by average loans held for investment	0.05%	0.04%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)	0.24%	0.21%
Retail banking
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 39	$ 54
Percentage annualized net charge-off by average loans held for investment	1.07%	1.46%