Securities-Net Securities Gains (Losses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Disclosure Net Securities Gains Losses [Abstract]
Realized gross gains	$ 57	$ 80	$ 62
Realized gross losses	(5)	(1)	0
Recognized gross impairments	(4)	(29)	(22)
Net securities gains	$ 48	$ 50	$ 40

This item represents the total realized gain (loss) included in earnings for the period as a result of selling marketable securities categorized as available-for-sale or held-to-maturity. Additionally, this item would include any losses recognized for other than temporary impairments of the subject investments in debt and equity securities.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration