Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (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
Unrealized net losses on hedges arising during the period, Before Tax Amount			$ 77	$ (15)
Less: reclassification adjustment for net losses on hedges included in net income, Before Tax Amount			(10)	10
Net change in unrealized losses on hedges, Before Tax Amount			67	(5)
Unrealized holding gains arising during the period on securities available for sale, Before Tax Amount			189	165
Reclassification adjustment for net gains on securities available for sale included in net income, Before Tax Amount			(88)	(58)
Reclassification of unrealized loss on securities held to maturity transferred to available for sale, Before Tax Amount			301
Less: accretion of fair value adjustment on securities available for sale, Before Tax Amount.			(2)	(5)
Less: accretion of privatization - related fair value adjustment on held-to-maturity securities, Before Tax Amount			(23)	(21)
Less: accretion of net unrealized losses on held-to-maturity securities, Before Tax Amount			84	77
Net change in unrealized losses on securities, Before Tax Amount			461	158
Foreign currency translation adjustment, Before Tax Amount			2	(2)
Amortization of transition amount, Before Tax Amount			1	1
Recognized net actuarial loss, Before Tax Amount			74	38
Pension and other benefits, Before Tax Amount				9
Pension and other benefits, Tax Effect				(4)
Pension and other benefits, Net of Tax				5
Net change in pension and other benefits, Before Tax Amount			75	48
Unrealized net losses on hedges arising during the period, Tax Effect			(30)	6
Net change in accumulated other comprehensive loss, Before Tax Amount			605	199
Less: reclassification adjustment for net losses on hedges included in net income, Tax Effect			4	(4)
Net change in unrealized losses on hedges, Tax Effect			(26)	2
Unrealized holding gains arising during the period on securities available for sale, Tax Effect			(74)	(65)
Reclassification adjustment for net gains on securities available for sale included in net income, Tax Effect			35	23
Reclassification of unrealized loss on securities held to maturity transferred to available for sale, Tax Effect			(118)
Less: accretion of fair value adjustment on securities available for sale, Tax Effect			1	2
Less: accretion of privatization - related fair value adjustment on held-to-maturity securities, Tax Effect			9	8
Less: accretion of net unrealized losses on held-to-maturity securities, Tax Effect			(33)	(30)
Net change in unrealized losses on securities, Tax Effect			(180)	(62)
Foreign currency translation adjustment, Tax Effect			(1)	1
Amortization of transition amount, Tax Effect
Recognized net actuarial loss, Tax Effect			(29)	(15)
Net change in pension and other benefits, Tax Effect			(29)	(19)
Unrealized net losses on hedges arising during the period, Net of Tax			47	(9)
Net change in accumulated other comprehensive loss, Tax Effect			(236)	(78)
Less: reclassification adjustment for net losses on hedges included in net income, Net of Tax			(6)	6
Net change in unrealized losses on hedges, Net of Tax	21	(3)	41	(3)
Unrealized holding gains arising during the period on securities available for sale, Net of Tax			115	100
Reclassification adjustment for net gains on securities available for sale included in net income			(53)	(35)
Reclassification of unrealized loss on securities held to maturity transferred to available for sale			183
Less: accretion of fair value adjustment on securities available for sale, Net of Tax			(1)	(3)
Less: accretion of privatization - related fair value adjustment on held-to-maturity securities, Net of Tax			(14)	(13)
Less: accretion of net unrealized losses on held-to-maturity securities, Net of Tax			51	47
Net change in unrealized losses on securities, Net of Tax	195	54	281	96
Foreign currency translation adjustment, Net of Tax	1	(2)	1	(1)
Amortization of transition amount, Net of Tax			1	1
Recognized net actuarial loss, Net of Tax			45	23
Net change in pension and other benefits, Net of Tax	16	8	46	29
Total other comprehensive income	$ 233	$ 57	$ 369	$ 121