Bank Line of Credit (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		1 Months Ended
	Nov. 30, 2011 Indemnity Y	Sep. 30, 2011 Indemnity	Oct. 31, 2011 Exchange Y holding partnership	Oct. 28, 2011 Exchange	Sep. 30, 2011 Exchange
Bank Line of Credit
Maximum borrowing capacity under the line of credit		$ 100		$ 300	$ 200
Fair value of bonds pledged as collateral on the line of credit		$ 137			$ 262
Term of revolving credit facility (in years)	5
Extension term of revolving credit facility (in years)			5