Activity of the Components of Other Comprehensive Income and Accumulated Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 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 period	$ 141	$ 113
Reclassification adjustment for net (gains) losses included in net income	(8)	(3)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	34	10
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(10)	(7)
Net activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	(2)	(1)
Total Other Comprehensive Activity
Pre-tax activity total	242	175
Total, Tax	(83)	(61)
Other comprehensive income (loss)	159	114
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	429	82
Other comprehensive income (loss), Net of Tax	159	114
Total Accumulated Other Comprehensive Income - Ending Balance	588	196
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	215	173
Reclassification adjustment for net losses (gains) included in net income	(12)	(5)
Net unrealized gains on available-for-sale securities	203	168
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	(74)	(60)
Reclassification adjustment for net losses (gains) included in net income	4	2
Net unrealized gains on available-for-sale securities	(70)	(58)
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	141	113
Reclassification adjustment for net (gains) losses included in net income	(8)	(3)
Net unrealized gains on available-for-sale securities	133	110
Total Other Comprehensive Activity
Other comprehensive income (loss)	133	110
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	475	121
Other comprehensive income (loss), Net of Tax	133	110
Total Accumulated Other Comprehensive Income - Ending Balance	608	231
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	52	15
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(16)	(10)
Net unrealized gains on cash flow hedge derivatives	36	5
Tax effect for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	(18)	(5)
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	6	3
Net unrealized gains on cash flow hedge derivatives	(12)	(2)
Net activity for net unrealized gain (loss) on cash flow hedge derivatives
Unrealized holding gains (losses) on cash flow hedge derivatives arising during period	34	10
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	(10)	(7)
Net unrealized gains on cash flow hedge derivatives	24	3
Total Other Comprehensive Activity
Other comprehensive income (loss)	24	3
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	23	13
Other comprehensive income (loss), Net of Tax	24	3
Total Accumulated Other Comprehensive Income - Ending Balance	47	16
Accumulated Defined Benefit Plans Adjustment
Pre-tax activity for defined benefit plans, net
Reclassification of amounts to net periodic benefit costs	3	2
Defined benefit plans, net	3	2
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	2	1
Defined benefit plans, net	2	1
Total Other Comprehensive Activity
Other comprehensive income (loss)	(2)	(1)
Total Accumulated Other Comprehensive Income
Total Accumulated Other Comprehensive Income - Beginning Balance	(69)	(52)
Other comprehensive income (loss), Net of Tax	(2)	(1)
Total Accumulated Other Comprehensive Income - Ending Balance	$ (67)	$ (51)