Loans - Consumer Banking: Net Charge-Offs and Nonperforming Loans (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Nonperforming loans	$ 753		$ 813
Nonperforming loans rate	0.30%		0.30%
Consumer Banking
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 221	$ 223
Net charge-offs rate	1.49%	1.19%
Nonperforming loans	$ 352		$ 479
Nonperforming loans rate	0.59%		0.81%
Consumer Banking | Auto
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 203	$ 208
Net charge-offs rate	1.44%	1.53%
Nonperforming loans	$ 321		$ 449
Nonperforming loans rate	0.57%		0.80%
Consumer Banking | Home loan
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 0	$ (1)
Net charge-offs rate	0.00%	(0.03%)
Consumer Banking | Retail banking
Loans and Leases Receivable Disclosure [Line Items]
Net charge-offs	$ 18	$ 16
Net charge-offs rate	2.56%	1.89%
Nonperforming loans	$ 31		$ 30
Nonperforming loans rate	1.10%		1.04%