Loss And Loss Adjustment Expense Reserves (Schedule OF Losses And Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	$ 409	$ 404
Insurance Loss Recoverable	486	504
Loss and loss adjustment expense reserves	559	541
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	559	541
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	486	504
U S Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	197	174
Loss and loss adjustment expense reserves	106	97
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	409	404
Insurance Loss Recoverable	289	330
Loss and loss adjustment expense reserves	453	444
International And Structured Finance Insurance [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	(911)	(221)
Loss and loss adjustment expense reserves	(234)	(206)
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	409	404
Insurance Loss Recoverable	1,200	551
Loss and loss adjustment expense reserves	$ 687	$ 650