AOCI (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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 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	$ (113)	$ 208	$ 538	$ 64
Reclassification adjustment for net (gains) losses included in net income	(1)	(7)	(11)	(11)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(15)	42	49	71
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(7)	(13)	(23)	(36)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	3	1	3	3
Reclassification of amounts to net periodic benefit costs	(5)	(2)	(8)	(8)
Total Other Comprehensive Activity
Pre-tax activity total	(182)	356	884	144
Total, Tax	48	(125)	(326)	(51)
Other comprehensive income (loss)	(134)	231	558	93
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	889	291	197	429
Other comprehensive income (loss), Net of Tax	(134)	231	558	93
Total Accumulated Other Comprehensive Income - Ending Balance	755	522	755	522
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	(149)	319	855	98
Reclassification adjustment for net losses (gains) included in net income	(2)	(10)	(18)	(16)
Net unrealized gains on available-for-sale securities	(151)	309	837	82
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	36	(111)	(317)	(34)
Reclassification adjustment for net losses (gains) included in net income	1	3	7	5
Net unrealized gains on available-for-sale securities	37	(108)	(310)	(29)
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	(113)	208	538	64
Reclassification adjustment for net (gains) losses included in net income	(1)	(7)	(11)	(11)
Net unrealized gains on available-for-sale securities	(114)	201	527	53
Total Other Comprehensive Activity
Other comprehensive income (loss)	(114)	201	527	53
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	879	327	238	475
Other comprehensive income (loss), Net of Tax	(114)	201	527	53
Total Accumulated Other Comprehensive Income - Ending Balance	765	528	765	528
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	(23)	65	77	109
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(11)	(20)	(37)	(55)
Net unrealized gains on cash flow hedge derivatives	(34)	45	40	54
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	8	(23)	(28)	(38)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	4	7	14	19
Net unrealized gains on cash flow hedge derivatives	12	(16)	(14)	(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	(15)	42	49	71
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(7)	(13)	(23)	(36)
Net unrealized gains on cash flow hedge derivatives	(22)	29	26	35
Total Other Comprehensive Activity
Other comprehensive income (loss)	(22)	29	26	35
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	70	29	22	23
Other comprehensive income (loss), Net of Tax	(22)	29	26	35
Total Accumulated Other Comprehensive Income - Ending Balance	48	58	48	58
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial loss	(5)	(1)	(5)	(4)
Reclassification of amounts to net periodic benefit costs	8	3	12	12
Defined benefit plans, net	3	2	7	8
Tax effect for defined benefit plans, net
Net actuarial loss	2	0	2	1
Reclassification of amounts to net periodic benefit costs	(3)	(1)	(4)	(4)
Defined benefit plans, net	(1)	(1)	(2)	(3)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	(3)	(1)	(3)	(3)
Reclassification of amounts to net periodic benefit costs	5	2	8	8
Defined benefit plans, net	2	1	5	5
Total Other Comprehensive Activity
Other comprehensive income (loss)	(2)	(1)	(5)	(5)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(60)	(65)	(63)	(69)
Other comprehensive income (loss), Net of Tax	(2)	(1)	(5)	(5)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (58)	$ (64)	$ (58)	$ (64)