Fair Value Measurements and Derivative Instruments (Details) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of investment securities	$ 990,000,000	$ 861,000,000
Subsidiary ILC total investments	316,000,000	282,000,000
Subsidiary ILC cash and cash equivalents	27,000,000	28,000,000
Subsidiary ILC short term investments	33,000,000	11,000,000
Subsidiary ILC long term investments	256,000,000	243,000,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds / commercial paper	346,024,000	239,157,000
Equity securities	0	0
Commingled fixed income securities	0	0
Debt securities - U.S. and foreign governments, agencies and municipalities	123,302,000	93,175,000
Debt securities - corporate	0	0
Mortgage-back / asset-back securities	0	0
Interest rate swaps	0	0
Foreign exchange contracts	0	0
Total assets	469,326,000	332,332,000
Foreign exchange contracts	0	0
Total liabilities	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds / commercial paper	283,575,000	300,702,000
Equity securities	24,888,000	22,097,000
Commingled fixed income securities	28,152,000	27,747,000
Debt securities - U.S. and foreign governments, agencies and municipalities	19,288,000	19,042,000
Debt securities - corporate	33,820,000	31,467,000
Mortgage-back / asset-back securities	136,322,000	134,262,000
Interest rate swaps	14,468,000	15,465,000
Foreign exchange contracts	900,000	4,230,000
Total assets	541,413,000	555,012,000
Foreign exchange contracts	(4,144,000)	(1,439,000)
Total liabilities	(4,144,000)	(1,439,000)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds / commercial paper	0	0
Equity securities	0	0
Commingled fixed income securities	0	0
Debt securities - U.S. and foreign governments, agencies and municipalities	0	0
Debt securities - corporate	0	0
Mortgage-back / asset-back securities	0	0
Interest rate swaps	0	0
Foreign exchange contracts	0	0
Total assets	0	0
Foreign exchange contracts	0	0
Total liabilities	0	0
Total Level [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds / commercial paper	629,599,000	539,859,000
Equity securities	24,888,000	22,097,000
Commingled fixed income securities	28,152,000	27,747,000
Debt securities - U.S. and foreign governments, agencies and municipalities	142,590,000	112,217,000
Debt securities - corporate	33,820,000	31,467,000
Mortgage-back / asset-back securities	136,322,000	134,262,000
Interest rate swaps	14,468,000	15,465,000
Foreign exchange contracts	900,000	4,230,000
Total assets	1,010,739,000	887,344,000
Foreign exchange contracts	(4,144,000)	(1,439,000)
Total liabilities	(4,144,000)	(1,439,000)
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	(4,260,628,000)	(4,233,909,000)
Portion at Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	$ (4,419,066,000)	$ (4,364,176,000)