Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions			12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loans and Leases Receivable Disclosure [Line Items]
Nonperforming Loans	$ 1,599	$ 1,170	$ 1,599	$ 1,170
Financing Receivable, Nonaccrual, Percent Past Due	0.65%	0.51%
Consumer Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 820	$ 731	$ 675
Percentage annualized net charge-off by average loans held for investment			1.15%	1.03%
Nonperforming Loans	$ 527	$ 558	$ 527	$ 558
Financing Receivable, Nonaccrual, Percent Past Due	0.72%	0.79%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			1.49%	1.45%
Nonperforming loans, excluding acquired loans (as percent)	0.90%	1.08%
Consumer Portfolio Segment [Member] | Auto
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 752	$ 674
Percentage annualized net charge-off by average loans held for investment			1.69%	1.69%
Nonperforming Loans	$ 223	$ 219	$ 223	$ 219
Financing Receivable, Nonaccrual, Percent Past Due	0.47%	0.53%
Consumer Portfolio Segment [Member] | Home loan
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 14	$ 9
Percentage annualized net charge-off by average loans held for investment			0.06%	0.03%
Nonperforming Loans	$ 273	$ 311	$ 273	$ 311
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)			0.20%	0.13%
Nonperforming loans, excluding acquired loans (as percent)	3.81%	4.68%
Consumer Portfolio Segment [Member] | Retail banking
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 54	$ 48
Percentage annualized net charge-off by average loans held for investment			1.53%	1.33%
Nonperforming Loans	$ 31	$ 28	$ 31	$ 28
Financing Receivable, Nonaccrual, Percent Past Due	0.86%	0.77%