Goodwill and Other Intangible Assets - Summary of the Key Characteristics, Inputs, and Economic Assumptions Used to Estimate the Fair Value of the Company's MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Document Period End Date			Sep. 30, 2015
Servicing Asset at Fair Value, Amount	$ 1,262		$ 1,262		$ 1,206
Bank Servicing Fees	40	$ 44	$ 113	$ 143
Mortgage Servicing Rights, Fair Value [Member]
Prepayment rate assumption (annual)			11.00%	11.00%
Decline in fair value from 10% adverse change	51		$ 51		46
Decline in fair value from 20% adverse change	98		$ 98		88
Discount rate (annual)			8.00%	10.00%
Decline in fair value from 10% adverse change	55		$ 55		55
Decline in fair value from 20% adverse change	105		$ 105		105
Weighted-average life (in years)			6 years 5 months	6 years 5 months
Weighted-average coupon			4.10%	4.20%
indirect auto loan servicing rights [Member]
Servicing Asset at Fair Value, Amount	11		$ 11
Bank Servicing Fees	2	0	3	$ 0
Servicing Asset at Fair Value, Amount	(11)		(11)
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount	1,262	1,305	1,262	1,305	$ 1,206	$ 1,300
Bank Servicing Fees	$ 89	$ 81	254	$ 241
Unpaid Principal Balance of Outstanding Underlying MSRs Transferred			$ 10,300