Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	$ 37		$ (38)		$ 7
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	378		(295)		(63)
Reclassification adjustment for net gains included in net income	(24)		4		(10)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	39		(8)		24
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(29)		(29)		(54)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	25		(25)		5
Reclassification of amounts to net periodic benefit costs	(8)		(10)		(13)
Total Other Comprehensive Activity
Pre-tax activity total	534		(451)		(145)
Total, Tax	(187)		158		50
Other Comprehensive Income (Loss) Net Of Tax	347		(293)		(95)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	82		375		470
Other comprehensive income (loss), Net of Tax	347		(293)		(95)
Total Accumulated Other Comprehensive Income - Ending Balance	429		82		375
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	580		(454)		(97)
Reclassification adjustment for net losses (gains) included in net income	(37)	[1]	6	[1]	(15)
Net unrealized gains on available-for-sale securities	543		(448)		(112)
Tax effect for accumulated net unrealized gain (loss) on available-for-sale securities
Unrealized holding gains on available-for-sale securities arising during period	(202)		159		34
Reclassification adjustment for net losses (gains) included in net income	13		(2)		5
Net unrealized gains on available-for-sale securities	(189)		157		39
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	378		(295)		(63)
Reclassification adjustment for net gains included in net income	(24)		4		(10)
Net unrealized gains on available-for-sale securities	354		(291)		(73)
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax	354		(291)		(73)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	121		412		485
Other comprehensive income (loss), Net of Tax	354		(291)		(73)
Total Accumulated Other Comprehensive Income - Ending Balance	475		121		412
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	60		(13)		37
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(44)		(44)		(83)
Net unrealized gains on cash flow hedge derivatives	16		(57)		(46)
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains on cash flow hedge derivatives arising during period	(21)		5		(13)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	15		15		29
Net unrealized gains on cash flow hedge derivatives	(6)		20		16
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	39		(8)		24
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(29)		(29)		(54)
Net unrealized gains on cash flow hedge derivatives	10		(37)		(30)
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax	10		(37)		(30)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	13		50		80
Other comprehensive income (loss), Net of Tax	10		(37)		(30)
Total Accumulated Other Comprehensive Income - Ending Balance	23		13		50
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	(37)		38		(7)
Reclassification of amounts to net periodic benefit costs	12		16		20
Defined benefit plans, net	(25)		54		13
Tax effect for defined benefit plans, net
Net actuarial (gain) loss arising during the period	12		(13)		2
Reclassification of amounts to net periodic benefit costs	(4)		(6)		(7)
Defined benefit plans, net	8		(19)		(5)
Net activity for defined benefit plans, net
Net actuarial gain (loss) arising during the period	(25)		25		(5)
Reclassification of amounts to net periodic benefit costs	8		10		13
Defined benefit plans, net	(17)		35		8
Total Other Comprehensive Activity
Other Comprehensive Income (Loss) Net Of Tax	17		(35)		(8)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(52)		(87)		(95)
Other comprehensive income (loss), Net of Tax	17		(35)		(8)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (69)		$ (52)		$ (87)

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