Derivative Instruments and Hedging Activities (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Instrument and Hedging Activities (Textual) [Abstract]
Forecasted debt issuance variable rate period	3-month LIBOR
Average fixed rate on interest rate swaps	2.80%
Interest rate swap agreement, notional amount	$ 400,000,000
Companies matured fixed rate debt	791,000,000
Percentage of interest rate swap effectiveness	100.00%
Interest rate of fixed rate debt	5.875%
Interest rate swap recorded in other comprehensive income	23,000,000
Number of interest rate swap agreement	2
Increase Decrease in Interest expense due to amortization of gain on discontinuation of interest rate swap agreement	$ 10,000,000	$ 11,000,000	$ 10,000,000