Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			$ 375	$ 470
Total			(348)	(23)
Total			122	7
Unrealized holding gains (losses) on available-for-sale securities arising during period	(211)	(10)	(247)	(3)
Reclassification adjustment for net gains included in net income	33	(2)	38	(6)
Unrealized holding (losses) gains on cash flow hedge derivatives arising during period	(2)	10	(1)	16
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income	(6)	(14)	(20)	(27)
Net actuarial loss	2	2	4	4
Other comprehensive income (loss)	(184)	(14)	(226)	(16)
Accumulated other comprehensive income	149	454	149	454
Total Accumulated Other Comprehensive Income - Ending Balance	149	454	149	454
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			(380)	(4)
Reclassification adjustment for net losses (gains) included in net income			58	(10)
Net unrealized gains on available-for-sale securities			(322)	(14)
Unrealized holding losses on available-for-sale securities arising during period			133	1
Reclassification adjustment for net losses (gains) included in net income			20	(4)
Net unrealized gains on available-for-sale securities			113	5
Unrealized holding gains (losses) on available-for-sale securities arising during period			(247)	(3)
Reclassification adjustment for net gains included in net income			38	(6)
Net unrealized gains on available-for-sale securities			(209)	(9)
Other comprehensive income (loss)			(209)	(9)
Accumulated other comprehensive income	203	476	203	476
Total Accumulated Other Comprehensive Income - Ending Balance	203	476	203	476
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)	25
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(31)	(41)
Net unrealized gains on cash flow hedge derivatives			(32)	(16)
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period				(9)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(11)	(14)
Net unrealized gains on cash flow hedge derivatives			11	5
Unrealized holding (losses) gains on cash flow hedge derivatives arising during period			(1)	16
Reclassification adjustment for net (gains) losses on cash flow hedge derivatives included in net income			(20)	(27)
Net unrealized gains on cash flow hedge derivatives			(21)	(11)
Other comprehensive income (loss)			(21)	(11)
Accumulated other comprehensive income	29	69	29	69
Total Accumulated Other Comprehensive Income - Ending Balance	29	69	29	69
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			(87)	(95)
Net actuarial loss			(6)	(7)
Defined benefit plans, net			6	7
Net actuarial loss			2	3
Defined benefit plans, net			(2)	(3)
Net actuarial loss			(4)	(4)
Defined benefit plans, net			4	4
Other comprehensive income (loss)			(4)	(4)
Accumulated other comprehensive income	(83)	(91)	(83)	(91)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (83)	$ (91)	$ (83)	$ (91)