Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized holding gains arising during the period, Before Tax	$ 424	$ 70
Reclassification adjustment for net realized gains included in net income, Before Tax	63	64
Net unrealized gains recognized in other comprehensive income or loss, Before Tax	361	6
Postretirement benefit gain not yet recognized in net income arising during the period, Before Tax		2
Reclassification adjustment for the amortization of net actuarial loss and prior service cost included in net income, Before Tax	(9)	(24)
Net change in postretirement benefit costs not yet recognized in net income, Before Tax	9	26
Foreign currency translation losses, Before Tax	(28)	(77)
Total other comprehensive income (loss), Before Tax	342	(45)
Net unrealized holding gains arising during the period, Income Tax	148	24
Reclassification adjustment for net realized gains included in net income, Income Tax	22	22
Net unrealized gains recognized in other comprehensive income or loss, Income Tax	126	2
Postretirement benefit gain 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)	(8)
Net change in postretirement benefit costs not yet recognized in net income, Income Tax	3	9
Foreign currency translation losses, Income Tax	(9)	(27)
Total other comprehensive income (loss), Income Tax	120	(16)
Net unrealized holding gains arising during the period, Net of Tax	276	46
Reclassification adjustment for net realized gains included in net income, Net of Tax	41	42
Net unrealized gains recognized in other comprehensive income or loss, Net of Tax	235	4
Postretirement benefit gain 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	(6)	(16)
Net change in postretirement benefit costs not yet recognized in net income, Net of Tax	6	17
Foreign currency translation losses, Net of Tax	(19)	(50)
Total Other Comprehensive Income (Loss) Net of Tax	$ 222	$ (29)