Derivatives and Hedging Activities - Pre-Tax Net Gains (Losses) on Fair Value Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative	$ 70	$ 33
Net Gains (Losses) on Hedged Item	(41)
Other Income [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative	41
Net Gains (Losses) on Hedged Item	(41)
Interest Expense [Member] | Interest Rate [Member]
Derivatives, Fair Value [Line Items]
Net Gains (Losses) on Derivative	$ 29	$ 33