Insurance In Force (Summary Of Components Of Financial Guarantee Net Premiums Earned, Including Premiums Assumed From And Ceded To Other Companies) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Insurance in Force [Abstract]
Direct	$ 305	$ 379	$ 407
Assumed	2	2	2
Gross	307	381	409
Ceded premiums earned	7	9	12
Premiums earned (net of ceded premiums of $7, $9 and $12)	$ 300	$ 372	$ 397