Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Loans and Leases Receivable Disclosure [Line Items]
Nonperforming Loans	$ 1,292	$ 1,599	$ 1,292		$ 1,292
Financing Receivable, Nonaccrual, Percent Past Due	0.53%	0.65%
Consumer Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 232	$ 146	$ 450	$ 329
Percentage annualized net charge-off by average loans held for investment			1.25%	0.83%	1.22%	0.93%
Nonperforming Loans	$ 565	$ 527	$ 565		$ 565
Financing Receivable, Nonaccrual, Percent Past Due	0.75%	0.72%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired, prior to change in accounting estimate (as percent)			0.99%		1.09%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			1.50%	1.09%	1.48%	1.24%
Nonperforming loans, excluding acquired loans (as percent)	0.90%	0.90%
Consumer Portfolio Segment [Member] | Uncollectible Receivables
Loans and Leases Receivable Disclosure [Line Items]
Percentage annualized net charge-off by average loans held for investment			0.26%		0.13%
Consumer Portfolio Segment [Member] | Auto
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 215	$ 130	$ 414	$ 298
Percentage annualized net charge-off by average loans held for investment			1.70%	1.20%	1.67%	1.39%
Nonperforming Loans	$ 273	$ 223	$ 273		$ 273
Financing Receivable, Nonaccrual, Percent Past Due	0.53%	0.47%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired, prior to change in accounting estimate (as percent)			1.32%		1.48%
Consumer Portfolio Segment [Member] | Auto | Uncollectible Receivables
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 48
Percentage annualized net charge-off by average loans held for investment			0.38%		0.19%
Consumer Portfolio Segment [Member] | Home loan
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 2	$ 5	$ 4	$ 8
Percentage annualized net charge-off by average loans held for investment			0.04%	0.09%	0.03%	0.07%
Nonperforming Loans	$ 259	$ 273	$ 259		$ 259
Financing Receivable, Nonaccrual, Percent Past Due	1.31%	1.26%
Percentage annualized net charge-off by average loans held for investment, excluding loans acquired (as percent)			0.10%	0.31%	0.09%	0.24%
Nonperforming loans, excluding acquired loans (as percent)	3.50%	3.81%
Consumer Portfolio Segment [Member] | Retail banking
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs			$ 15	$ 11	$ 32	$ 23
Percentage annualized net charge-off by average loans held for investment			1.71%	1.26%	1.81%	1.31%
Nonperforming Loans	$ 33	$ 31	$ 33		$ 33
Financing Receivable, Nonaccrual, Percent Past Due	0.96%	0.86%