Loss And Loss Adjustment Expense Reserves (Schedule OF Losses And Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	$ 407	$ 404
Insurance Loss Recoverable	483	504
Loss and loss adjustment expense reserves	714	541
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss and loss adjustment expense reserves	714	541
Insurance Loss Recoverable [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	483	504
U S Public Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	191	174
Loss and loss adjustment expense reserves	255	97
International And Structured Finance Insurance [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	407	404
Insurance Loss Recoverable	292	330
Loss and loss adjustment expense reserves	459	444
International And Structured Finance Insurance [Member] | Variable Interest Entity Primary Beneficiary [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Insurance Loss Recoverable	(1,296)	(221)
Loss and loss adjustment expense reserves	(231)	(206)
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loan repurchase commitments	407	404
Insurance Loss Recoverable	1,588	551
Loss and loss adjustment expense reserves	$ 690	$ 650