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, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Servicing Asset at Fair Value, Amount	$ 1,025	$ 899
Mortgage Servicing Rights, Fair Value [Member]
Prepayment rate assumption (annual)	14.00%	16.00%
Decline in fair value from 10% adverse change	47	50
Decline in fair value from 20% adverse change	90	95
Discount rate (annual)	11.00%	11.00%
Decline in fair value from 10% adverse change	44	37
Decline in fair value from 20% adverse change	$ 85	$ 70
Weighted-average life (in years)	5 years 7 months	4 years 11 months
Weighted-average coupon	4.60%	4.80%