Change in Fair Value of Financial Instruments for which the FVO has been Elected (Additional Information) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		3 Months Ended	12 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2012	Sep. 30, 2013
Income recognized upon the sale of loans	$ 83	$ 1
Fair Value, Inputs, Level 2 [Member] | Collateralized Loan Obligations [Member]
Fair Value, Option, Credit Risk, Gains (Losses) on Assets			0	10
Fair Value, Inputs, Level 2 [Member] | Commercial and Corporate Leveraged Loans [Member] | Trading Securities [Member]
Fair Value, Option, Credit Risk, Gains (Losses) on Assets		$ 2			$ 1