Accumulated Other Comprehensive Income - Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net unrealized holding (losses) arising during period, tax	$ 89	$ 470	$ 217	$ 602
Reclassification adjustment for (gains) realized in net income, tax	(20)	(20)	(60)	(43)
OTTI reclassification adjustment for losses realized in net income, tax			0	1
Net gains (losses) arising during period, tax	6	(86)	1	(114)
Reclassification adjustment for losses realized in net income, tax	2	2	5	4
Amortization of prior service cost and transition obligation included in net income, tax			$ 1	$ 1