AOCI (Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 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 the year	$ (371)		$ 21	$ (130)
Reclassification adjustment for net (gains) losses included in net income	9		4	(7)
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	169		(7)	19
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	2		(12)	(31)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	(1)		(1)	1
Reclassification of amounts to net periodic benefit costs	(7)		(7)	(12)
Total Other Comprehensive Activity
Pre-tax activity total	(246)		(1)	(209)
Total, Tax	63		15	71
Other comprehensive income (loss)	(183)	$ (183)	14	(138)	$ (138)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	73		59	197
Other comprehensive income (loss), Net of Tax	(183)	(183)	14	(138)	(138)
Total Accumulated Other Comprehensive Income - Ending Balance	(112)	(112)	73	59	59
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	(483)		14	(196)
Reclassification adjustment for net losses (gains) included in net income	(11)		(3)	11
Net unrealized gains on available-for-sale securities	(472)		17	(207)
Tax effect for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains on available-for-sale securities arising during period	112		7	66
Reclassification adjustment for net losses (gains) included in net income	(2)		1	4
Net unrealized gains on available-for-sale securities	110		8	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 the year	(371)		21	(130)
Reclassification adjustment for net (gains) losses included in net income	9		4	(7)
Net unrealized gains on available-for-sale securities	(362)		25	(137)
Total Other Comprehensive Activity
Other comprehensive income (loss)	(362)		25	(137)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	126	135	101	238
Other comprehensive income (loss), Net of Tax	(362)		25	(137)
Total Accumulated Other Comprehensive Income - Ending Balance	(227)	(227)	126	101	101
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	214		(11)	30
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	2		(19)	(48)
Net unrealized gains on cash flow hedge derivatives	216		(30)	(18)
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains on cash flow hedge derivatives arising during period	(45)		4	(11)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	0		7	17
Net unrealized gains on cash flow hedge derivatives	(45)		11	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	169		(7)	19
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	2		(12)	(31)
Net unrealized gains on cash flow hedge derivatives	171		(19)	(12)
Total Other Comprehensive Activity
Other comprehensive income (loss)	171		(19)	(12)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(9)	(11)	10	22
Other comprehensive income (loss), Net of Tax	171		(19)	(12)
Total Accumulated Other Comprehensive Income - Ending Balance	160	160	(9)	10	10
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	1		1	(2)
Reclassification of amounts to net periodic benefit costs	9		11	18
Defined benefit plans, net	10		12	16
Tax effect for defined benefit plans, net
Net actuarial loss	0		0	1
Reclassification of amounts to net periodic benefit costs	(2)		(4)	(6)
Defined benefit plans, net	(2)		(4)	(5)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	1		1	(1)
Reclassification of amounts to net periodic benefit costs	7		7	12
Defined benefit plans, net	8		8	11
Total Other Comprehensive Activity
Other comprehensive income (loss)	8		(8)	11
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(44)	(53)	(52)	(63)
Other comprehensive income (loss), Net of Tax	8		(8)	11
Total Accumulated Other Comprehensive Income - Ending Balance	$ (45)	$ (45)	$ (44)	$ (52)	$ (52)