Credit Risk (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012 item	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Credit Risk
Amount of restricted cash and investments released	$ 118
Termination payment received by primary mortgage insurer	49
Amount of restricted cash released to the Company	69
Cash received			30
Accounts receivable, unrestricted cash	39		39
Loss on reinsurance contract termination	21	16	21	16
Number of reinsurance agreements terminated		1
Summary of the activity in the liability for reinsurance losses
Balance, beginning of period			33	84
Realized losses			(35)	(51)
Increase in liability for reinsurance losses			2	10
Balance, end of period		43		43
Realized reinsurance losses related to release of reserves on termination of inactive reinsurance agreements			28	21
Receivables greater than 90 days past due and still accruing interest	3		3		5
Greater than 90 days	3		3		5
Allowance for credit losses	$ 0		$ 0		$ 0