AOCI (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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
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	$ 200	$ (285)	$ 652	$ (144)
Reclassification adjustment for net (gains) losses included in net income	(6)	4	(11)	(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	17	(5)	65	29
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(8)	(13)	(17)	(23)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(2)	(2)	(3)	(4)
Total Other Comprehensive Activity
Pre-tax activity total	318	(454)	1,067	(212)
Total, Tax	(113)	157	(375)	74
Other comprehensive income (loss)	205	(297)	692	(138)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	684	588	197	429
Other comprehensive income (loss), Net of Tax	205	(297)	692	(138)
Total Accumulated Other Comprehensive Income - Ending Balance	889	291	889	291
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	309	(436)	1,004	(221)
Reclassification adjustment for net losses (gains) included in net income	(8)	6	(16)	(6)
Net unrealized gains on available-for-sale securities	301	(430)	988	(227)
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	(109)	151	(352)	77
Reclassification adjustment for net losses (gains) included in net income	2	(2)	5	2
Net unrealized gains on available-for-sale securities	(107)	149	(347)	79
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	200	(285)	652	(144)
Reclassification adjustment for net (gains) losses included in net income	(6)	4	(11)	(4)
Net unrealized gains on available-for-sale securities	194	(281)	641	(148)
Total Other Comprehensive Activity
Other comprehensive income (loss)	194	(281)	641	(148)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	685	608	238	475
Other comprehensive income (loss), Net of Tax	194	(281)	641	(148)
Total Accumulated Other Comprehensive Income - Ending Balance	879	327	879	327
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	26	(8)	100	44
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(12)	(19)	(26)	(35)
Net unrealized gains on cash flow hedge derivatives	14	(27)	74	9
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(9)	3	(35)	(15)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	4	6	9	12
Net unrealized gains on cash flow hedge derivatives	(5)	9	(26)	(3)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	17	(5)	65	29
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(8)	(13)	(17)	(23)
Net unrealized gains on cash flow hedge derivatives	9	(18)	48	6
Total Other Comprehensive Activity
Other comprehensive income (loss)	9	(18)	48	6
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	61	47	22	23
Other comprehensive income (loss), Net of Tax	9	(18)	48	6
Total Accumulated Other Comprehensive Income - Ending Balance	70	29	70	29
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	3	3	5	6
Defined benefit plans, net	3	3	5	6
Tax effect for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(1)	(2)	(2)
Defined benefit plans, net	(1)	(1)	(2)	(2)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	2	2	3	4
Defined benefit plans, net	2	2	3	4
Total Other Comprehensive Activity
Other comprehensive income (loss)	(2)	(2)	(3)	(4)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(62)	(67)	(63)	(69)
Other comprehensive income (loss), Net of Tax	(2)	(2)	(3)	(4)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (60)	$ (65)	$ (60)	$ (65)