Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions			3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Nonperforming Loans	$ 1,578	$ 1,170	$ 1,578
Financing Receivable, Nonaccrual, Percent Past Due	0.69%	0.51%
Consumer Portfolio Segment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 183	$ 159
Percentage annualized net charge-off by average loans held for investment			1.04%	0.89%
Nonperforming Loans	$ 470	$ 558	$ 470
Financing Receivable, Nonaccrual, Percent Past Due	0.66%	0.79%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			1.40%	1.30%
Nonperforming loans, excluding acquired loans (as percent)	0.89%	1.08%
Consumer Portfolio Segment [Member] | Auto
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 168	$ 148
Percentage annualized net charge-off by average loans held for investment			1.60%	1.55%
Nonperforming Loans	$ 133	$ 219	$ 133
Financing Receivable, Nonaccrual, Percent Past Due	0.31%	0.53%
Consumer Portfolio Segment [Member] | Home loan
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 3	$ 2
Percentage annualized net charge-off by average loans held for investment			0.05%	0.03%
Nonperforming Loans	$ 307	$ 311	$ 307
Financing Receivable, Nonaccrual, Percent Past Due	1.26%	1.23%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			0.17%	0.11%
Nonperforming loans, excluding acquired loans (as percent)	4.55%	4.68%
Consumer Portfolio Segment [Member] | Retail banking
Financing Receivable, Allowance for Credit Losses [Line Items]
Net charge-offs			$ 12	$ 9
Percentage annualized net charge-off by average loans held for investment			1.36%	0.96%
Nonperforming Loans	$ 30	$ 28	$ 30
Financing Receivable, Nonaccrual, Percent Past Due	0.83%	0.77%