Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions			12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonperforming Loans	$ 1,170	$ 809	$ 1,170	$ 809
Financing Receivable, Nonaccrual, Percent Past Due	0.51%	0.39%
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 731	$ 675
Percentage annualized net charge-off by average loans held for investment			1.03%	0.95%
Nonperforming Loans	$ 558	$ 549	$ 558	$ 549
Financing Receivable, Nonaccrual, Percent Past Due	0.79%	0.77%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			1.45%	1.49%
Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 674	$ 619
Percentage annualized net charge-off by average loans held for investment			1.69%	1.78%
Nonperforming Loans	$ 219	$ 197	$ 219	$ 197
Financing Receivable, Nonaccrual, Percent Past Due	0.53%	0.52%
Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 9	$ 17
Percentage annualized net charge-off by average loans held for investment			0.03%	0.05%
Nonperforming Loans	$ 311	$ 330	$ 311	$ 330
Financing Receivable, Nonaccrual, Percent Past Due	1.23%	1.10%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			0.13%	0.24%
Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 48	$ 39
Percentage annualized net charge-off by average loans held for investment			1.33%	1.07%
Nonperforming Loans	$ 28	$ 22	$ 28	$ 22
Financing Receivable, Nonaccrual, Percent Past Due	0.77%	0.61%