Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net unrealized holding gains (losses) arising during the period, Before Tax	$ (573)	$ 436	$ (405)	$ 860
Reclassification adjustment for net realized gains included in net income, Before Tax	4	70	5	133
Net unrealized gains (losses) recognized in other comprehensive income, Before Tax	(577)	366	(410)	727
Postretirement benefit gain (loss) not yet recognized in net income arising during the year, Before Tax	(4)		5
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(16)	(8)	(32)	(17)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	12	8	37	17
Foreign currency translation gains (losses), Before Tax	23	6	(247)	(22)
Total other comprehensive income (loss), Before Tax	(542)	380	(620)	722
Net unrealized holding gains (losses) arising during the period, Income Tax	(200)	153	(142)	301
Reclassification adjustment for net realized gains included in net income, Income Tax	2	25	2	47
Net unrealized gains (losses) recognized in other comprehensive income, Income Tax	(202)	128	(144)	254
Postretirement benefit gain (loss) not yet recognized in net income arising during the year, Income Tax	(1)		2
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Income Tax	(6)	(3)	(11)	(6)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	5	3	13	6
Foreign currency translation gains (losses), Income Tax	8	2	(86)	(7)
Total other comprehensive income (loss), Income Tax	(189)	133	(217)	253
Net unrealized holding gains (losses) arising during the period, Net of Tax	(373)	283	(263)	559
Reclassification adjustment for net realized gains included in net income, Net of Tax	2	45	3	86
Net unrealized gains (losses) recognized in other comprehensive income, Net of Tax	(375)	238	(266)	473
Postretirement benefit gain (loss) not yet recognized in net income arising during the year, Net of Tax	(3)		3
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Net of Tax	(10)	(5)	(21)	(11)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	7	5	24	11
Foreign currency translation gains (losses), Net of Tax	15	4	(161)	(15)
Total Other Comprehensive Income (Loss) Net of Tax	$ (353)	$ 247	$ (403)	$ 469