Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder (Benefits) And Claims Incurred Net	$ 205	$ 50	$ 469	$ 149
Weighted average risk-free rate used to discount claim liability	2.17%
Insurance loss recoverable	$ 611		611		$ 504
Loss and loss adjustment expense reserves	818		818		541
Reinsurance Receivables Case Basis	15		15		6
Second Lien Residential Mortgage Backed Securities And Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder (Benefits) And Claims Incurred Net	54	44	58	78
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Policyholder (Benefits) And Claims Incurred Net	6	$ 6	33	$ 34
Loss and loss adjustment expense reserves	69		69		$ 60
Ineligible Mortgage Loans [Member] | Second Lien Residential Mortgage Backed Securities And Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Contract Claims On Ineligible Mortgage Loans Inception To Date Incurred Loss On Transactions	$ 435		$ 435