Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 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	$ 452	$ 141
Reclassification adjustment for net (gains) losses included in net income	(5)	(8)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	48	34
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(9)	(10)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(1)	(2)
Total Other Comprehensive Activity
Pre-tax activity total	749	242
Total, Tax	(262)	(83)
Other comprehensive income (loss)	487	159
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	197	429
Other comprehensive income (loss), Net of Tax	487	159
Total Accumulated Other Comprehensive Income - Ending Balance	684	588
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	695	215
Reclassification adjustment for net losses (gains) included in net income	(8)	(12)
Net unrealized gains on available-for-sale securities	687	203
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	(243)	(74)
Reclassification adjustment for net losses (gains) included in net income	3	4
Net unrealized gains on available-for-sale securities	(240)	(70)
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	452	141
Reclassification adjustment for net (gains) losses included in net income	(5)	(8)
Net unrealized gains on available-for-sale securities	447	133
Total Other Comprehensive Activity
Other comprehensive income (loss)	447	133
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	238	475
Other comprehensive income (loss), Net of Tax	447	133
Total Accumulated Other Comprehensive Income - Ending Balance	685	608
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	74	52
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(14)	(16)
Net unrealized gains on cash flow hedge derivatives	60	36
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(26)	(18)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	5	6
Net unrealized gains on cash flow hedge derivatives	(21)	(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	48	34
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(9)	(10)
Net unrealized gains on cash flow hedge derivatives	39	24
Total Other Comprehensive Activity
Other comprehensive income (loss)	39	24
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	22	23
Other comprehensive income (loss), Net of Tax	39	24
Total Accumulated Other Comprehensive Income - Ending Balance	61	47
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	2	3
Defined benefit plans, net	2	3
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	2
Defined benefit plans, net	1	2
Total Other Comprehensive Activity
Other comprehensive income (loss)	(1)	(2)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(63)	(69)
Other comprehensive income (loss), Net of Tax	(1)	(2)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (62)	$ (67)