Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total	$ (4)	$ (81)
Total	2	30
Total Accumulated Other Comprehensive Income - Beginning Balance	470	314
Unrealized holding gains (losses) on available-for-sale securities arising during period	7	(37)
Unrealized holding gains on cash flow hedge derivatives arising during period	6
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(9)
Net actuarial loss	3	2
Total	(2)	(51)
Total Accumulated Other Comprehensive Income - Ending Balance	468	263
Reclassification adjustment for net gains included in net income	(5)	(7)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding gains on available-for-sale securities arising during period	10	(57)
Reclassification adjustment for net gains included in net income	(7)	(12)
Net unrealized gains on available-for-sale securities	3	(69)
Unrealized holding gains on available-for-sale securities arising during period	(3)	20
Reclassification adjustment for net gains included in net income	2	5
Net unrealized gains on available-for-sale securities	(1)	25
Total Accumulated Other Comprehensive Income - Beginning Balance	485	321
Unrealized holding gains (losses) on available-for-sale securities arising during period	7	(37)
Net unrealized gains on available-for-sale securities	2	(44)
Total	2	(44)
Total Accumulated Other Comprehensive Income - Ending Balance	487	277
Reclassification adjustment for net gains included in net income	(5)	(7)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding gains on cash flow hedge derivatives arising during period	9
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(20)	(15)
Net unrealized gains on cash flow hedge derivatives	(11)	(15)
Unrealized holding gains on cash flow hedge derivatives arising during period	(3)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	7	6
Net unrealized gains on cash flow hedge derivatives	4	6
Total Accumulated Other Comprehensive Income - Beginning Balance	80	67
Unrealized holding gains on cash flow hedge derivatives arising during period	6
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(9)
Net unrealized gains on cash flow hedge derivatives	(7)	(9)
Total	(7)	(9)
Total Accumulated Other Comprehensive Income - Ending Balance	73	58
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net actuarial loss	4	3
Defined benefit plans, net	4	3
Net actuarial loss	(1)	(1)
Defined benefit plans, net	(1)	(1)
Total Accumulated Other Comprehensive Income - Beginning Balance	(95)	(74)
Net actuarial loss	3	2
Defined benefit plans, net	3	2
Total	3	2
Total Accumulated Other Comprehensive Income - Ending Balance	$ (92)	$ (72)