Loans - Consumer Banking: Net Charge-Offs (Detail) - Consumer Portfolio Segment [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 203	$ 190	$ 498	$ 460
Percentage annualized net charge-off by average loans held for investment	1.14%	1.07%	0.93%	0.87%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)	1.58%	1.65%	1.33%	1.37%
Auto
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 188	$ 176	$ 457	$ 421
Percentage annualized net charge-off by average loans held for investment	1.85%	1.98%	1.54%	1.65%
Home loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 1	$ 2	$ 6	$ 12
Percentage annualized net charge-off by average loans held for investment	0.01%	0.02%	0.03%	0.05%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)	0.05%	0.11%	0.11%	0.22%
Retail banking
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs	$ 14	$ 12	$ 35	$ 27
Percentage annualized net charge-off by average loans held for investment	1.53%	1.36%	1.30%	1.00%