AOCI (Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during the year		$ (130)	$ (227)	$ 378
Reclassification adjustment for net (gains) losses included in net income		(7)	(10)	(24)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during the year		19	48	39
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(31)	(49)	(29)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		1	5	25
Reclassification of amounts to net periodic benefit costs		(12)	(11)	(8)
Total Other Comprehensive Activity
Pre-tax activity total		(209)	(358)	534
Total, Tax		71	126	(187)
Other comprehensive income (loss)		(138)	(232)	347
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		197	429	82
Other comprehensive income (loss), Net of Tax		(138)	(232)	347
Total Accumulated Other Comprehensive Income - Ending Balance		59	197	429
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		(196)	(349)	580
Reclassification adjustment for net losses (gains) included in net income	[1]	(11)	(16)	(37)
Net unrealized gains on available-for-sale securities		(207)	(365)	543
Tax effect for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains on available-for-sale securities arising during period		66	122	(202)
Reclassification adjustment for net losses (gains) included in net income		4	6	13
Net unrealized gains on available-for-sale securities		70	128	(189)
Net activity for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains (losses) on available-for-sale securities arising during the year		(130)	(227)	378
Reclassification adjustment for net (gains) losses included in net income		(7)	(10)	(24)
Net unrealized gains on available-for-sale securities		(137)	(237)	354
Total Other Comprehensive Activity
Other comprehensive income (loss)		(137)	(237)	354
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		238	475	121
Other comprehensive income (loss), Net of Tax		(137)	(237)	354
Total Accumulated Other Comprehensive Income - Ending Balance		101	238	475
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		30	74	60
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(48)	(75)	(44)
Net unrealized gains on cash flow hedge derivatives		(18)	(1)	16
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains on cash flow hedge derivatives arising during period		(11)	(26)	(21)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		17	26	15
Net unrealized gains on cash flow hedge derivatives		6	0	(6)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during the year		19	48	39
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		(31)	(49)	(29)
Net unrealized gains on cash flow hedge derivatives		(12)	(1)	10
Total Other Comprehensive Activity
Other comprehensive income (loss)		(12)	(1)	10
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		22	23	13
Other comprehensive income (loss), Net of Tax		(12)	(1)	10
Total Accumulated Other Comprehensive Income - Ending Balance		10	22	23
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		(2)	(9)	(37)
Reclassification of amounts to net periodic benefit costs		18	17	12
Defined benefit plans, net		16	8	(25)
Tax effect for defined benefit plans, net
Net actuarial loss		1	4	12
Reclassification of amounts to net periodic benefit costs		(6)	(6)	(4)
Defined benefit plans, net		(5)	(2)	8
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period		(1)	(5)	(25)
Reclassification of amounts to net periodic benefit costs		12	11	8
Defined benefit plans, net		11	6	(17)
Total Other Comprehensive Activity
Other comprehensive income (loss)		(11)	(6)	17
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance		(63)	(69)	(52)
Other comprehensive income (loss), Net of Tax		(11)	(6)	17
Total Accumulated Other Comprehensive Income - Ending Balance		$ (52)	$ (63)	$ (69)

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