Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding gains on available-for-sale securities arising during period	$ 369	$ 357
Reclassification adjustment for net gains included in net income	(64)	(24)
Net unrealized gains on available-for-sale securities	305	333
Unrealized holding gains on cash flow hedge derivatives arising during period	59	(2)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(21)	(46)
Net unrealized gains on cash flow hedge derivatives	38	(48)
Net actuarial loss	8	9
Defined benefit plans, net	8	9
Total	351	294
Unrealized holding gains on available-for-sale securities arising during period	(126)	(126)
Reclassification adjustment for net gains included in net income	19	9
Net unrealized gains on available-for-sale securities	(107)	(117)
Unrealized holding gains on cash flow hedge derivatives arising during period	(20)	1
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	7	16
Net unrealized gains on cash flow hedge derivatives	(13)	17
Net actuarial loss	(3)	(3)
Defined benefit plans, net	(3)	(3)
Total	(123)	(103)
Total Accumulated Other Comprehensive Income - Beginning Balance	314
Unrealized holding gains on available-for-sale securities arising during period	243	231
Reclassification adjustment for net gains included in net income	(45)	(15)
Net unrealized gains on available-for-sale securities	198	216
Unrealized holding gains on cash flow hedge derivatives arising during period	39	(1)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(14)	(30)
Net unrealized gains on cash flow hedge derivatives	25	(31)
Net actuarial loss	5	6
Defined benefit plans, net	5	6
Total	228	191
Total Accumulated Other Comprehensive Income - Ending Balance	542	432
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income - Beginning Balance	321	216
Net unrealized gains on available-for-sale securities	519
Total	198	216
Total Accumulated Other Comprehensive Income - Ending Balance		432
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income - Beginning Balance	67	105
Total	25	(31)
Total Accumulated Other Comprehensive Income - Ending Balance	92	74
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income - Beginning Balance	(74)	(80)
Total	5	6
Total Accumulated Other Comprehensive Income - Ending Balance	$ (69)	$ (74)