Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net unrealized holding gains (losses) arising during the period, Before Tax	$ (6)	$ (10)	$ 854	$ (896)
Reclassification adjustment for net realized gains (losses) included in net income, Before Tax	65	(5)	198	179
Net unrealized gains (losses) recognized in other comprehensive income or loss, Before Tax	(71)	(5)	656	(1,075)
Postretirement benefit gain not yet recognized in net income arising during the period, Before Tax	1	1	1	2
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(9)	(23)	(26)	(70)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	10	24	27	72
Foreign currency translation losses, Before Tax	(40)	(64)	(62)	(99)
Total other comprehensive Income (loss), Before Tax	(101)	(45)	621	(1,102)
Net unrealized holding gains (losses) arising during the period, Income Tax	(3)	(3)	298	(313)
Reclassification adjustment for net realized gains (losses) included in net income, Income Tax	22	(1)	69	63
Net unrealized gains (losses) recognized in other comprehensive income or loss, Income Tax	(25)	(2)	229	(376)
Postretirement benefit gain not yet recognized in net income arising during the period, Income Tax		1		1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Income Tax	(4)	(8)	(10)	(25)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	4	9	10	26
Foreign currency translation losses, Income Tax	(14)	(23)	(21)	(36)
Total other comprehensive Income (loss), Income Tax	(35)	(16)	218	(386)
Net unrealized holding gains (losses) arising during the period, Net of Tax	(3)	(7)	556	(583)
Reclassification adjustment for net realized gains included in net income, Net of Tax	43	(4)	129	116
Net unrealized gains (losses) recognized in other comprehensive income or loss, Net of Tax	(46)	(3)	427	(699)
Postretirement benefit gain (loss) not yet recognized in net income arising during the period, Net of Tax	1		1	1
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Net of Tax	(5)	(15)	(16)	(45)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	6	15	17	46
Foreign currency translation gains losses, Net of Tax	(26)	(41)	(41)	(63)
Total Other Comprehensive Income (Loss) Net of Tax	$ (66)	$ (29)	$ 403	$ (716)