Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		$ 9	$ 37	$ (38)
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		(227)	378	(295)
Reclassification adjustment for net gains included in net income		(10)	(24)	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		48	39	(8)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(49)	(29)	(29)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		5	25	(25)
Reclassification of amounts to net periodic benefit costs		(11)	(8)	(10)
Total Other Comprehensive Activity
Pre-tax activity total		(358)	534	(451)
Total, Tax		126	(187)	158
Other Comprehensive Income (Loss) Net Of Tax		(232)	347	(293)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		429	82	375
Other comprehensive income (loss), Net of Tax		(232)	347	(293)
Total Accumulated Other Comprehensive Income - Ending Balance		197	429	82
Accumulated Net Unrealized Investment Gain (Loss)
Pre-tax activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains on available-for-sale securities arising during period		(349)	580	(454)
Reclassification adjustment for net losses (gains) included in net income	[1]	(16)	(37)	6
Net unrealized gains on available-for-sale securities		(365)	543	(448)
Tax effect for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains on available-for-sale securities arising during period		122	(202)	159
Reclassification adjustment for net losses (gains) included in net income		6	13	(2)
Net unrealized gains on available-for-sale securities		128	(189)	157
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		(227)	378	(295)
Reclassification adjustment for net gains included in net income		(10)	(24)	4
Net unrealized gains on available-for-sale securities		(237)	354	(291)
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax		(237)	354	(291)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		475	121	412
Other comprehensive income (loss), Net of Tax		(237)	354	(291)
Total Accumulated Other Comprehensive Income - Ending Balance		238	475	121
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 on cash flow hedge derivatives arising during period		74	60	(13)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(75)	(44)	(44)
Net unrealized gains on cash flow hedge derivatives		(1)	16	(57)
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains on cash flow hedge derivatives arising during period		(26)	(21)	5
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		26	15	15
Net unrealized gains on cash flow hedge derivatives			(6)	20
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	39	(8)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(49)	(29)	(29)
Net unrealized gains on cash flow hedge derivatives		(1)	10	(37)
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax		(1)	10	(37)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		23	13	50
Other comprehensive income (loss), Net of Tax		(1)	10	(37)
Total Accumulated Other Comprehensive Income - Ending Balance		22	23	13
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		(9)	(37)	38
Reclassification of amounts to net periodic benefit costs		17	12	16
Defined benefit plans, net		8	(25)	54
Tax effect for defined benefit plans, net
Net actuarial (gain) loss arising during the period		4	12	(13)
Reclassification of amounts to net periodic benefit costs		(6)	(4)	(6)
Defined benefit plans, net		(2)	8	(19)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		(5)	(25)	25
Reclassification of amounts to net periodic benefit costs		11	8	10
Defined benefit plans, net		6	(17)	35
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax		(6)	17	(35)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		(69)	(52)	(87)
Other comprehensive income (loss), Net of Tax		(6)	17	(35)
Total Accumulated Other Comprehensive Income - Ending Balance		$ (63)	$ (69)	$ (52)

[1] Amounts in parentheses indicate reductions to net income.