Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (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
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			$ 470	$ 314
Total			(4)
Total			2
Unrealized holding gains (losses) on available-for-sale securities arising during period	22	155	19	243
Reclassification adjustment for net gains included in net income	(4)	(34)	(10)	(45)
Unrealized holding gains on cash flow hedge derivatives arising during period	8	17	23	39
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income	(14)	6	(41)	(14)
Net actuarial loss	2	2	7	5
Other comprehensive income (loss)	14	146	(2)	228
Accumulated other comprehensive income	468	542	468	542
Total Accumulated Other Comprehensive Income - Ending Balance	468	542	468	542
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			485	321
Unrealized holding gains on available-for-sale securities arising during period			29	369
Reclassification adjustment for net gains included in net income			(16)	(64)
Net unrealized gains on available-for-sale securities			13	305
Unrealized holding gains on available-for-sale securities arising during period			(10)	(126)
Reclassification adjustment for net gains included in net income			6	19
Net unrealized gains on available-for-sale securities			(4)	(107)
Unrealized holding gains (losses) on available-for-sale securities arising during period			19	243
Reclassification adjustment for net gains included in net income			(10)	(45)
Net unrealized gains on available-for-sale securities			9	198
Other comprehensive income (loss)			9	198
Accumulated other comprehensive income	494	519	494	519
Total Accumulated Other Comprehensive Income - Ending Balance	494	519	494	519
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			80	67
Unrealized holding gains on cash flow hedge derivatives arising during period			35	59
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(63)	(21)
Net unrealized gains on cash flow hedge derivatives			(28)	38
Unrealized holding gains on cash flow hedge derivatives arising during period			(12)	(20)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			22	7
Net unrealized gains on cash flow hedge derivatives			10
Unrealized holding gains on cash flow hedge derivatives arising during period			23	39
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income			(41)	(14)
Net unrealized gains on cash flow hedge derivatives			(18)	25
Other comprehensive income (loss)			(18)	25
Accumulated other comprehensive income	62	92	62	92
Total Accumulated Other Comprehensive Income - Ending Balance	62	92	62	92
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			(95)	(74)
Net actuarial loss			11	8
Defined benefit plans, net			11
Net actuarial loss			(4)	(3)
Defined benefit plans, net			(4)
Net actuarial loss			7	5
Defined benefit plans, net			7
Other comprehensive income (loss)			7	5
Accumulated other comprehensive income	(88)	(69)	(88)	(69)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (88)	$ (69)	$ (88)	$ (69)