Comprehensive Income - Components of Other Comprehensive Income or Loss (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized holding gains arising during the period, Before tax	$ 70
Reclassification adjustment for net realized gains (Losses) included in net income, Before tax	64
Net unrealized gains recognized in other comprehensive income or loss, Before tax	6
Postretirement benefit costs 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, Before tax	(24)
Net change in postretirement benefit costs not yet recognized in net income, Before tax	26
Foreign currency translation losses, Before tax	(77)
Total other comprehensive loss, Before tax	(45)
Net unrealized holding gains arising during the period, Income tax	24
Reclassification adjustment for net realized gains included in net income, Income tax	22
Net unrealized gains recognized in other comprehensive income or loss, Income tax	2
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, Income tax	(8)
Net change in postretirement benefit costs not yet recognized in net income, Income tax	9
Foreign currency translation losses, Income tax	(27)
Total other comprehensive loss, Income tax	(16)
Net unrealized holding gains arising during the period, Net of tax	46
Reclassification adjustment for net realized gains included in net income, Net of tax	42
Net unrealized gains recognized in other comprehensive income or loss, Net of tax	4
Postretirement benefit costs 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, Net of tax	(16)
Net change in postretirement benefit costs not yet recognized in net income, Net of tax	17	14
Foreign currency translation losses, Net of tax	(50)	(9)
Total Other Comprehensive Income (Loss) Net of Tax	$ (29)	$ 60