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, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance	$ 375	$ 470
Total	(66)	(4)
Total	24	2
Unrealized holding gains (losses) on available-for-sale securities arising during period	(36)	7
Reclassification adjustment for net gains included in net income	5	(5)
Unrealized holding gains on cash flow hedge derivatives arising during period	1	6
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income	(14)	(13)
Net actuarial loss	2	3
Other comprehensive income (loss)	(42)	(2)
Accumulated other comprehensive income	333	468
Total Accumulated Other Comprehensive Income - Ending Balance	333	468
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance	412	485
Unrealized holding gains on available-for-sale securities arising during period	(56)	10
Reclassification adjustment for net gains included in net income	7	(7)
Net unrealized gains on available-for-sale securities	(49)	3
Unrealized holding gains on available-for-sale securities arising during period	20	(3)
Reclassification adjustment for net gains included in net income	2	(2)
Net unrealized gains on available-for-sale securities	18	(1)
Unrealized holding gains (losses) on available-for-sale securities arising during period	(36)	7
Reclassification adjustment for net gains included in net income	5	(5)
Net unrealized gains on available-for-sale securities	(31)	2
Other comprehensive income (loss)	(31)	2
Accumulated other comprehensive income	381	487
Total Accumulated Other Comprehensive Income - Ending Balance	381	487
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance	50	80
Unrealized holding gains on cash flow hedge derivatives arising during period	1	9
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(21)	(20)
Net unrealized gains on cash flow hedge derivatives	(20)	(11)
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)	7
Net unrealized gains on cash flow hedge derivatives	7	4
Unrealized holding gains on cash flow hedge derivatives arising during period	1	6
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income	(14)	(13)
Net unrealized gains on cash flow hedge derivatives	(13)	(7)
Other comprehensive income (loss)	(13)	(7)
Accumulated other comprehensive income	37	73
Total Accumulated Other Comprehensive Income - Ending Balance	37	73
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance	(87)	(95)
Net actuarial loss	(3)	(4)
Defined benefit plans, net	3	4
Net actuarial loss	1	1
Defined benefit plans, net	(1)	(1)
Net actuarial loss	(2)	(3)
Defined benefit plans, net	2	3
Other comprehensive income (loss)	(2)	(3)
Accumulated other comprehensive income	(85)	(92)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (85)	$ (92)