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, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			$ 470	$ 314
Total			(23)	125
Total			7	(43)
Unrealized holding gains (losses) on available-for-sale securities arising during period	(10)	125	(3)	88
Reclassification adjustment for net gains included in net income	(2)	(4)	(6)	(11)
Unrealized holding gains on cash flow hedge derivatives arising during period	10	21	16	21
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(14)	(11)	(27)	(20)
Net actuarial loss	2	2	4	4
Other comprehensive loss	(14)	133	(16)	82
Accumulated other comprehensive income	454	396	454	396
Total Accumulated Other Comprehensive Income - Ending Balance	454	396	454	396
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			(4)	135
Reclassification adjustment for net gains included in net income			(10)	(17)
Net unrealized gains on available-for-sale securities			(14)	118
Unrealized holding gains on available-for-sale securities arising during period			1	(47)
Reclassification adjustment for net gains included in net income			4	6
Net unrealized gains on available-for-sale securities			5	(41)
Unrealized holding gains (losses) on available-for-sale securities arising during period			(3)	88
Reclassification adjustment for net gains included in net income			(6)	(11)
Net unrealized gains on available-for-sale securities			(9)	77
Other comprehensive loss			(9)	77
Accumulated other comprehensive income	476	398	476	398
Total Accumulated Other Comprehensive Income - Ending Balance	476	398	476	398
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			25	32
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(41)	(31)
Net unrealized gains on cash flow hedge derivatives			(16)	1
Unrealized holding gains on cash flow hedge derivatives arising during period			(9)	11
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			14	(11)
Net unrealized gains on cash flow hedge derivatives			5
Unrealized holding gains on cash flow hedge derivatives arising during period			16	21
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income			(27)	(20)
Net unrealized gains on cash flow hedge derivatives			(11)	1
Other comprehensive loss			(11)	1
Accumulated other comprehensive income	69	68	69	68
Total Accumulated Other Comprehensive Income - Ending Balance	69	68	69	68
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss)
Total Accumulated Other Comprehensive Income - Beginning Balance			(95)	(74)
Net actuarial loss			7	6
Defined benefit plans, net			7	6
Net actuarial loss			(3)	(2)
Defined benefit plans, net			(3)	(2)
Net actuarial loss			4	4
Defined benefit plans, net			4	4
Other comprehensive loss			4	4
Accumulated other comprehensive income	(91)	(70)	(91)	(70)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (91)	$ (70)	$ (91)	$ (70)