Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during period	$ 208	$ (69)	$ 64	$ 233
Reclassification adjustment for net (gains) losses included in net income	(7)	(3)	(11)	(16)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	42	(3)	71	19
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(7)	(36)	(20)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	1		3
Reclassification of amounts to net periodic benefit costs	(2)	(1)	(8)	(3)
Total Other Comprehensive Activity
Pre-tax activity total	356	(122)	144	336
Total, Tax	(125)	41	(51)	(117)
Other comprehensive income (loss)	231	(81)	93	219
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		382	429	82
Other comprehensive income (loss), Net of Tax	231	(81)	93	219
Total Accumulated Other Comprehensive Income - Ending Balance	522	301	522	301
Accumulated Net Unrealized Investment Gain (Loss)
Pre-tax activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during period	319	(105)	98	357
Reclassification adjustment for net losses (gains) included in net income	(10)	(5)	(16)	(25)
Net unrealized gains on available-for-sale securities	309	(110)	82	332
Tax effect for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during period	(111)	36	(34)	(124)
Reclassification adjustment for net losses (gains) included in net income	3	2	5	9
Net unrealized gains on available-for-sale securities	(108)	38	(29)	(115)
Net activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during period	208	(69)	64	233
Reclassification adjustment for net (gains) losses included in net income	(7)	(3)	(11)	(16)
Net unrealized gains on available-for-sale securities	201	(72)	53	217
Total Other Comprehensive Activity
Other comprehensive income (loss)	201	(72)	53	217
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	327	410	475	121
Other comprehensive income (loss), Net of Tax	201	(72)	53	217
Total Accumulated Other Comprehensive Income - Ending Balance	528	338	528	338
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Pre-tax activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	65	(4)	109	30
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(20)	(10)	(55)	(31)
Net unrealized gains on cash flow hedge derivatives	45	(14)	54	(1)
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(23)	1	(38)	(11)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	7	3	19	11
Net unrealized gains on cash flow hedge derivatives	(16)	4	(19)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	42	(3)	71	19
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(7)	(36)	(20)
Net unrealized gains on cash flow hedge derivatives	29	(10)	35	(1)
Total Other Comprehensive Activity
Other comprehensive income (loss)	29	(10)	35	(1)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	29	22	23	13
Other comprehensive income (loss), Net of Tax	29	(10)	35	(1)
Total Accumulated Other Comprehensive Income - Ending Balance	58	12	58	12
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial loss	(1)		(4)
Reclassification of amounts to net periodic benefit costs	3	2	12	5
Defined benefit plans, net	2	2	8	5
Tax effect for defined benefit plans, net
Net actuarial loss			1
Reclassification of amounts to net periodic benefit costs	(1)	(1)	(4)	(2)
Defined benefit plans, net	(1)	(1)	(3)	(2)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	(1)		(3)
Reclassification of amounts to net periodic benefit costs	2	1	8	3
Defined benefit plans, net	1	1	5	3
Total Other Comprehensive Activity
Other comprehensive income (loss)	(1)	(1)	(5)	(3)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(65)	(50)	(69)	(52)
Other comprehensive income (loss), Net of Tax	(1)	(1)	(5)	(3)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (64)	$ (49)	$ (64)	$ (49)