Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized holding gains (losses)arising during the year, Before Tax	$ (1,000)	$ 556	$ 1,029
Unrealized other-than-temporary impairment losses arising during the year, Before Tax		(2)	(1)
Reclassification adjustment for net realized gains included in net income, Before tax	212	127	81
Net unrealized gains (losses) recognized in other comprehensive income or loss, Before Tax	(1,212)	427	947
Postretirement benefit gain (loss) not yet recognized in net income arising during the year, Before Tax	622	(128)	(400)
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(93)	(83)	(71)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	715	(45)	(329)
Foreign currency translation gains (losses), Before Tax	(111)	(16)	6
Total other comprehensive income (loss), Before Tax	(608)	366	624
Net unrealized holding gains (losses) arising during the year, Income Tax	(350)	195	359
Unrealized other-than-temporary impairment losses arising during the year, Income Tax		(1)
Reclassification adjustment for net realized gains included in net income, Income Tax	74	44	28
Net unrealized gains (losses) recognized in other comprehensive income or loss, Income Tax	(424)	150	331
Postretirement benefit gain (loss) not yet recognized in net income arising during the year, Income Tax	218	(45)	(140)
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Income Tax	(33)	(30)	(26)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	251	(15)	(114)
Foreign currency translation gains (losses), Income Tax	(39)	(5)	2
Total other comprehensive income (loss), Income Tax	(212)	130	219
Net unrealized holding losses arising during the period, Net of Tax	(650)	361	670
Unrealized other-than-temporary impairment losses arising during the year, Net of Tax		(1)	(1)
Reclassification adjustment for net realized gains included in net income, Net of Tax	138	83	53
Net unrealized gains (losses) recognized in other comprehensive income or loss, Net of Tax	(788)	277	616
Postretirement benefit gain (loss) not yet recognized in net income arising during the period, Net of Tax	404	(83)	(260)
Reclassification adjustment for the amortization of net actuarial loss and prior service cost, Net of Tax	(60)	(53)	(45)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	464	(30)	(215)
Foreign currency translation gains (losses), Net of Tax	(72)	(11)	4
Total Other Comprehensive Income (Loss) Net of Tax	$ (396)	$ 236	$ 405