Fair Value Measurements Debt at at Carrying and Fair Value (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Liabilities:
Total long-term debt	$ 5,904,334,000	$ 5,892,440,000
Carrying Value [Member] | Level 2 [Member]
Liabilities:
Notes Receivable, Fair Value Disclosure	52,000,000.0	52,700,000
Subsidiaries [Member]
Liabilities:
Total long-term debt	4,338,523,000	4,338,044,000
Discounted cash flow [Member] | Fair Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	7,296,847,000	7,980,646,000
Discounted cash flow [Member] | Fair Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	7,063,347,000	7,755,946,000
Long-term debt (variable-rate)	233,500,000	224,700,000
Discounted cash flow [Member] | Carrying Value [Member]
Liabilities:
Long-term Debt, Excluding Current Maturities, Fair Value Disclosure	5,904,334,000	5,892,440,000
Discounted cash flow [Member] | Carrying Value [Member] | Level 2 [Member]
Liabilities:
Long-term debt (fixed-rate), net of discount	5,670,834,000	5,667,740,000
Long-term debt (variable-rate)	233,500,000	224,700,000
Debt issuance costs	21,900,000	22,700,000
Discounted cash flow [Member] | Subsidiaries [Member] | Fair Value [Member]
Liabilities:
Total long-term debt	5,446,409,000	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	5,446,409,000	6,086,358,000
Discounted cash flow [Member] | Subsidiaries [Member] | Carrying Value [Member]
Liabilities:
Total long-term debt	4,338,523,000	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	4,338,523,000	4,338,044,000
Debt issuance costs	$ 22,600,000	$ 22,900,000