Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions			3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Nonperforming Loans	$ 1,362	$ 1,599	$ 1,362
Financing Receivable, Nonaccrual, Percent Past Due	0.57%	0.65%
Consumer Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 218	$ 183
Percentage annualized net charge-off by average loans held for investment			1.19%	1.04%
Nonperforming Loans	$ 471	$ 527	$ 471
Financing Receivable, Nonaccrual, Percent Past Due	0.64%	0.72%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			1.46%	1.40%
Nonperforming loans, excluding acquired loans (as percent)	0.78%	0.90%
Consumer Portfolio Segment [Member] | Auto
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 199	$ 168
Percentage annualized net charge-off by average loans held for investment			1.64%	1.60%
Nonperforming Loans	$ 179	$ 223	$ 179
Financing Receivable, Nonaccrual, Percent Past Due	0.36%	0.47%
Consumer Portfolio Segment [Member] | Home loan
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 2	$ 3
Percentage annualized net charge-off by average loans held for investment			0.03%	0.05%
Nonperforming Loans	$ 264	$ 273	$ 264
Financing Receivable, Nonaccrual, Percent Past Due	1.27%	1.26%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			0.08%	0.17%
Nonperforming loans, excluding acquired loans (as percent)	3.64%	3.81%
Consumer Portfolio Segment [Member] | Retail banking
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 17	$ 12
Percentage annualized net charge-off by average loans held for investment			1.92%	1.36%
Nonperforming Loans	$ 28	$ 31	$ 28
Financing Receivable, Nonaccrual, Percent Past Due	0.82%	0.86%