AOCI (Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	$ 15	$ 452	[1]
Reclassification adjustment for net (gains) losses included in net income	1	(5)	[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	(3)	48	[1]
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(5)	(9)	[1]
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(1)	[1]
Total Other Comprehensive Activity
Pre-tax activity total	13	749
Total, Tax	(4)	(262)
Other comprehensive income (loss)	9	487	[1]
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	59	197
Other comprehensive income (loss), Net of Tax	9	487	[1]
Total Accumulated Other Comprehensive Income - Ending Balance	68	684
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	22	695
Reclassification adjustment for net losses (gains) included in net income	2	(8)
Net unrealized gains on available-for-sale securities	24	687
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	(7)	(243)
Reclassification adjustment for net losses (gains) included in net income	(1)	3
Net unrealized gains on available-for-sale securities	(8)	(240)
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	15	452
Reclassification adjustment for net (gains) losses included in net income	1	(5)
Net unrealized gains on available-for-sale securities	16	447
Total Other Comprehensive Activity
Other comprehensive income (loss)	16	447
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	101	238
Other comprehensive income (loss), Net of Tax	16	447
Total Accumulated Other Comprehensive Income - Ending Balance	117	685
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	(5)	74
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(8)	(14)
Net unrealized gains on cash flow hedge derivatives	(13)	60
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	2	(26)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	3	5
Net unrealized gains on cash flow hedge derivatives	5	(21)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(3)	48
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(5)	(9)
Net unrealized gains on cash flow hedge derivatives	(8)	39
Total Other Comprehensive Activity
Other comprehensive income (loss)	(8)	39
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	10	22
Other comprehensive income (loss), Net of Tax	(8)	39
Total Accumulated Other Comprehensive Income - Ending Balance	2	61
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	2	2
Defined benefit plans, net	2	2
Tax effect for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(1)
Defined benefit plans, net	(1)	(1)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	1	1
Defined benefit plans, net	1	1
Total Other Comprehensive Activity
Other comprehensive income (loss)	(1)	(1)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(52)	(63)
Other comprehensive income (loss), Net of Tax	(1)	(1)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (51)	$ (62)

[1] A net tax deficiency of $1 million was reclassified from capital surplus to applicable income tax expense at March 31, 2016, related to the early adop tion of ASU 2016-09 during the fourth quarter of 2016, with an effective date of January 1, 2016.