Variable Interest Entities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Variable Interest Entity [Line Items]
Carrying amounts of assets	$ 17,633	$ 22,132	$ 17,633	$ 22,132	$ 21,724
Carrying amounts of liabilities	14,432		14,432		18,530
Number of variable interest entities consolidated	0	0	0	0
Net realized gains (losses) related to deconsolidation	1	0	1	0
Variable Interest Entity Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Carrying amounts of assets	6,400		6,400		8,300
Carrying amounts of liabilities	5,400		5,400		7,300
Variable Interest Entity Non Primary Beneficiary [Member] | Financial Intermediary [Member]
Variable Interest Entity [Line Items]
VIE Assets	$ 144		$ 144