Debt (Secured Tower Revenue Securities Series 2010) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Proceeds from issuance of 2010 Tower Securities, net of fees paid				$ 1,212,256,000
4.254% Secured Tower Revenue Securities Series 2010-1 [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Proceeds from issuance of 2010 Tower Securities, net of fees paid			680,000,000
Tower Revenue Securities, annual interest rate			4.254%
Tower Revenue Securities anticipated repayment date			April 16, 2015
Tower Revenue Securities maturity date			April 16, 2040
5.101% Secured Tower Revenue Securities Series 2010-2 [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Proceeds from issuance of 2010 Tower Securities, net of fees paid			550,000,000
Tower Revenue Securities, annual interest rate			5.101%
Tower Revenue Securities anticipated repayment date			April 16, 2017
Tower Revenue Securities maturity date			April 16, 2042
Tower Securities [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Weighted average annual fixed coupon interest rate	4.60%		4.60%
Interest expense on 2010 Tower Revenue Securities	$ 14,300,000	$ 14,300,000	$ 43,000,000	$ 26,300,000