Fair Value Measurements Debt at at Carrying and Fair Value (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Liabilities:
Total long-term debt	$ 6,203,182,000	$ 5,892,440,000
Carrying Value [Member] | Level 2 [Member]
Liabilities:
Notes Receivable, Fair Value Disclosure	53,000,000.0	52,700,000
Subsidiaries [Member]
Liabilities:
Total long-term debt	4,339,003,000	4,338,044,000
Discounted cash flow [Member] | Fair Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	8,008,100,000	7,980,646,000
Discounted cash flow [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	7,975,400,000	7,755,946,000
Long-term debt (variable-rate)	32,700,000	224,700,000
Discounted cash flow [Member] | Carrying Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	6,203,182,000	5,892,440,000
Discounted cash flow [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	6,170,482,000	5,667,740,000
Long-term debt (variable-rate)	32,700,000	224,700,000
Debt issuance costs	21,600,000	22,700,000
Discounted cash flow [Member] | Subsidiaries [Member] | Fair Value [Member]
Liabilities:
Total long-term debt	5,833,823,000	6,086,358,000
Discounted cash flow [Member] | Subsidiaries [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	5,833,823,000	6,086,358,000
Discounted cash flow [Member] | Subsidiaries [Member] | Carrying Value [Member]
Liabilities:
Total long-term debt	4,339,003,000	4,338,044,000
Discounted cash flow [Member] | Subsidiaries [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	4,339,003,000	4,338,044,000
Debt issuance costs	$ 22,200,000	$ 22,900,000