Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized holding gains (losses) arising during the period, Before Tax	$ 436	$ (956)	$ 860	$ (886)
Reclassification adjustment for net realized gains included in net income, Before Tax	70	120	133	184
Net unrealized gains (losses) recognized in other comprehensive income, Before Tax	366	(1,076)	727	(1,070)
Postretirement benefit costs not yet recognized in net income arising during the period, Before Tax		(1)		1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(8)	(23)	(17)	(47)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	8	22	17	48
Foreign currency translation gains (losses), Before Tax	6	42	(22)	(35)
Total other comprehensive Income (loss), Before Tax	380	(1,012)	722	(1,057)
Net unrealized holding gains (losses) arising during the period, Income Tax	153	(334)	301	(310)
Reclassification adjustment for net realized gains included in net income, Income Tax	25	42	47	64
Net unrealized gains (losses) recognized in other comprehensive income, Income Tax	128	(376)	254	(374)
Postretirement benefit costs not yet recognized in net income arising during the period, Income Tax		(1)
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Income Tax	(3)	(9)	(6)	(17)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	3	8	6	17
Foreign currency translation gains (losses), Income Tax	2	14	(7)	(13)
Total other comprehensive Income (loss), Income Tax	133	(354)	253	(370)
Net unrealized holding gains (losses) arising during the period, Net of Tax	283	(622)	559	(576)
Reclassification adjustment for net realized gains included in net income, Net of Tax	45	78	86	120
Net unrealized gains (losses) recognized in other comprehensive income or loss, Net of Tax	238	(700)	473	(696)
Postretirement benefit gain (loss) not yet recognized in net income arising during the period, Net of Tax				1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Net of Tax	(5)	(14)	(11)	(30)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	5	14	11	31
Foreign currency translation gains (losses), Net of Tax	4	28	(15)	(22)
Total Other Comprehensive Income (Loss) Net of Tax	$ 247	$ (658)	$ 469	$ (687)