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, 2017	Jun. 30, 2016		Jun. 30, 2017	Jun. 30, 2016
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	$ 93	$ 200	[1]	$ 108	$ 652	[1]
Reclassification adjustment for net (gains) losses included in net income	0	(6)	[1]	1	(11)	[1]
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	17	[1]	2	65	[1]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(4)	(8)	[1]	(9)	(17)	[1]
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(2)	[1]	(2)	(3)	[1]
Total Other Comprehensive Activity
Pre-tax activity total	152	318		164	1,067
Total, Tax	(57)	(113)		(60)	(375)
Other comprehensive income (loss)	95	205	[1]	104	692	[1]
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	68	684		59	197
Other comprehensive income (loss), Net of Tax	95	205	[1]	104	692	[1]
Total Accumulated Other Comprehensive Income - Ending Balance	163	889		163	889
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	148	309		170	1,004
Reclassification adjustment for net losses (gains) included in net income	0	(8)		2	(16)
Net unrealized gains on available-for-sale securities	148	301		172	988
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	(55)	(109)		(62)	(352)
Reclassification adjustment for net losses (gains) included in net income	0	2		(1)	5
Net unrealized gains on available-for-sale securities	(55)	(107)		(63)	(347)
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	93	200		108	652
Reclassification adjustment for net (gains) losses included in net income	0	(6)		1	(11)
Net unrealized gains on available-for-sale securities	93	194		109	641
Total Other Comprehensive Activity
Other comprehensive income (loss)	93	194		109	641
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	117	685		101	238
Other comprehensive income (loss), Net of Tax	93	194		109	641
Total Accumulated Other Comprehensive Income - Ending Balance	210	879		210	879
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	26		3	100
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(6)	(12)		(14)	(26)
Net unrealized gains on cash flow hedge derivatives	2	14		(11)	74
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)	(9)		(1)	(35)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	2	4		5	9
Net unrealized gains on cash flow hedge derivatives	(1)	(5)		4	(26)
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	17		2	65
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(4)	(8)		(9)	(17)
Net unrealized gains on cash flow hedge derivatives	1	9		(7)	48
Total Other Comprehensive Activity
Other comprehensive income (loss)	1	9		(7)	48
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	2	61		10	22
Other comprehensive income (loss), Net of Tax	1	9		(7)	48
Total Accumulated Other Comprehensive Income - Ending Balance	3	70		3	70
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	2	3		3	5
Defined benefit plans, net	2	3		3	5
Tax effect for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(1)		(1)	(2)
Defined benefit plans, net	(1)	(1)		(1)	(2)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	1	2		2	3
Defined benefit plans, net	1	2		2	3
Total Other Comprehensive Activity
Other comprehensive income (loss)	(1)	(2)		(2)	(3)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(51)	(62)		(52)	(63)
Other comprehensive income (loss), Net of Tax	(1)	(2)		(2)	(3)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (50)	$ (60)		$ (50)	$ (60)

[1] Net tax deficiencies of $5 and $6 were reclassified from capital surplus to applicable income tax expense for the three and six months ended June 30, 2016, respectively, related to the early adoption of ASU 2016-09 during the fourth quarter of 2016, with an ef fective date of January 1, 2016.