Changes in Liability for Policy an Contract Claims (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in reserves	$ 2,524	[1]	$ 2,386	[1]
Strengthened reserve as a result of changes in estimates related to prior year insured events	629	[2]	(74)	[2]
U.S. Mortgage Insurance
Liability for Claims and Claims Adjustment Expense [Line Items]
Strengthened reserve as a result of changes in estimates related to prior year insured events	23
U.S. Mortgage Insurance | Loss Mitigation
Liability for Claims and Claims Adjustment Expense [Line Items]
Strengthened reserve as a result of changes in estimates related to prior year insured events	257		408
U.S. Mortgage Insurance | Loss Mitigation | Workouts Loan Modifications and Pre Sales
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in reserves	26		31
Strengthened reserve as a result of changes in estimates related to prior year insured events	250		398
U.S. Mortgage Insurance | Loss Mitigation | Rescissions
Liability for Claims and Claims Adjustment Expense [Line Items]
Strengthened reserve as a result of changes in estimates related to prior year insured events	7		10
U.S. Mortgage Insurance | Loss Mitigation | Reinstatements
Liability for Claims and Claims Adjustment Expense [Line Items]
Strengthened reserve as a result of changes in estimates related to prior year insured events	$ 1		$ 11

[1] For the nine months ended September 30, 2014, current year reserves related to our U.S. Mortgage Insurance segment were reduced by loss mitigation activities of $26 million related to workouts, loan modifications and pre-sales. For the nine months ended September 30, 2013, current year reserves related to our U.S. Mortgage Insurance segment were reduced by loss mitigation activities of $31 million related to workouts, loan modifications and pre-sales.

[2] Loss mitigation actions related to prior year delinquencies resulted in a reduction of expected losses in prior year reserves of $257 million for the nine months ended September 30, 2014, including $250 million related to workouts, loan modifications and pre-sales, and $7 million related to rescissions, net of reinstatements of $1 million. Loss mitigation actions related to prior year delinquencies resulted in a reduction of expected losses in prior year reserves of $408 million for the nine months ended September 30, 2013, including $398 million related to workouts, loan modifications and pre-sales, and $10 million related to rescissions, net of reinstatements of $11 million.