Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net unrealized holding gains (losses) arising during the period, Before Tax	$ 2	$ (6)	$ (403)	$ 854
Reclassification adjustment for net realized gains included in net income, Before Tax	31	65	36	198
Net unrealized gains (losses) recognized in other comprehensive income or loss, Before Tax	(29)	(71)	(439)	656
Postretirement benefit gain not yet recognized in net income arising during the period, Before Tax	2	1	7	1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(15)	(9)	(47)	(26)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	17	10	54	27
Foreign currency translation losses, Before Tax	(58)	(40)	(305)	(62)
Total other comprehensive income (loss), Before Tax	(70)	(101)	(690)	621
Net unrealized holding gains (losses) arising during the period, Income Tax	1	(3)	(141)	298
Reclassification adjustment for net realized gains included in net income, Income Tax	11	22	13	69
Net unrealized gains (losses) recognized in other comprehensive income or loss, Income Tax	(10)	(25)	(154)	229
Postretirement benefit gain not yet recognized in net income arising during the period, Income Tax			2
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Income Tax	(6)	(4)	(17)	(10)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	6	4	19	10
Foreign currency translation losses, Income Tax	(20)	(14)	(106)	(21)
Total other comprehensive income (loss), Income Tax	(24)	(35)	(241)	218
Net unrealized holding gains (losses) arising during the period, Net of Tax	1	(3)	(262)	556
Reclassification adjustment for net realized gains included in net income, Net of Tax	20	43	23	129
Net unrealized gains (losses) recognized in other comprehensive income or loss, Net of Tax	(19)	(46)	(285)	427
Postretirement benefit gain not yet recognized in net income arising during the period, Net of Tax	2	1	5	1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Net of Tax	(9)	(5)	(30)	(16)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	11	6	35	17
Foreign currency translation losses, Net of Tax	(38)	(26)	(199)	(41)
Total Other Comprehensive Income (Loss) Net of Tax	$ (46)	$ (66)	$ (449)	$ 403