Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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	$ (285)	$ 188	$ (144)	$ 301
Reclassification adjustment for net (gains) losses included in net income	4	(9)	(4)	(12)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(5)	12	29	22
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(6)	(23)	(13)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(2)	(1)	(4)	(2)
Total Other Comprehensive Activity
Pre-tax activity total	(454)	283	(212)	458
Total, Tax	157	(97)	74	(158)
Other comprehensive income (loss)	(297)	186	(138)	300
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		196	429	82
Other comprehensive income (loss), Net of Tax	(297)	186	(138)	300
Total Accumulated Other Comprehensive Income - Ending Balance	291	382	291	382
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	(436)	288	(221)	461
Reclassification adjustment for net losses (gains) included in net income	6	(14)	(6)	(19)
Net unrealized gains on available-for-sale securities	(430)	274	(227)	442
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	151	(100)	77	(160)
Reclassification adjustment for net losses (gains) included in net income	(2)	5	2	7
Net unrealized gains on available-for-sale securities	149	(95)	79	(153)
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	(285)	188	(144)	301
Reclassification adjustment for net (gains) losses included in net income	4	(9)	(4)	(12)
Net unrealized gains on available-for-sale securities	(281)	179	(148)	289
Total Other Comprehensive Activity
Other comprehensive income (loss)	(281)	179	(148)	289
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	608	231	475	121
Other comprehensive income (loss), Net of Tax	(281)	179	(148)	289
Total Accumulated Other Comprehensive Income - Ending Balance	327	410	327	410
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	(8)	19	44	34
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(19)	(11)	(35)	(21)
Net unrealized gains on cash flow hedge derivatives	(27)	8	9	13
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	3	(7)	(15)	(12)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	6	5	12	8
Net unrealized gains on cash flow hedge derivatives	9	(2)	(3)	(4)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(5)	12	29	22
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(13)	(6)	(23)	(13)
Net unrealized gains on cash flow hedge derivatives	(18)	6	6	9
Total Other Comprehensive Activity
Other comprehensive income (loss)	(18)	6	6	9
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	47	16	23	13
Other comprehensive income (loss), Net of Tax	(18)	6	6	9
Total Accumulated Other Comprehensive Income - Ending Balance	29	22	29	22
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	3	1	6	3
Defined benefit plans, net	3	1	6	3
Tax effect for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)		(2)	(1)
Defined benefit plans, net	(1)		(2)	(1)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	2	1	4	2
Defined benefit plans, net	2	1	4	2
Total Other Comprehensive Activity
Other comprehensive income (loss)	(2)	(1)	(4)	(2)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(67)	(51)	(69)	(52)
Other comprehensive income (loss), Net of Tax	(2)	(1)	(4)	(2)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (65)	$ (50)	$ (65)	$ (50)