SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION CONDENSED CONSOLIDATING FINANCIAL STATEMENTS, Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Cash provided by operating activities	$ 1,315,412	$ 1,353,341	$ 1,022,828
Investing activities
Capital expenditures	(512,393)	(624,634)	(1,188,312)
Contributions to unconsolidated affiliates	(87,861)	(68,275)	(27,540)
Other investing activities	0	0	(12,607)
Cash provided by (used in) investing activities	(567,633)	(615,445)	(1,190,719)
Financing activities
Dividends paid	(829,414)	(517,601)	(509,197)
Distributions to noncontrolling interests	(276,260)	(549,419)	(535,825)
Borrowing (repayment) of short-term borrowings, net	(495,604)	563,937	(508,956)
Issuance of long-term debt, net of discounts	1,190,496	1,000,000	1,291,506
Debt financing costs	(11,425)	(2,770)	(17,515)
Repayment of long-term debt	(994,776)	(1,108,040)	(7,753)
Issuance of common stock	471,358	21,971	20,669
Issuance of common units, net of issuance costs	0	0	375,660
Other	(13,836)	5,403	(15,848)
Cash provided by (used in) financing activities	(959,461)	(586,519)	92,741
Change in cash and cash equivalents	(211,682)	151,377	(75,150)
Change in cash and cash equivalents included in discontinued operations	0	(121)	(43)
Change in cash and cash equivalents included in continuing operations	(211,682)	151,256	(75,193)
Cash and cash equivalents at beginning of period	248,875	97,619	172,812
Cash and cash equivalents at end of period	37,193	248,875	97,619
Reportable Legal Entities | Parent Issuer & Guarantor
Operating activities
Cash provided by operating activities	947,400	717,000	650,300
Investing activities
Capital expenditures	0	(200)	(100)
Contributions to unconsolidated affiliates	0		(671,000)
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	(200)	(671,100)
Financing activities
Dividends paid	(829,400)	(517,600)	(509,200)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	(2,500,700)	(63,100)	4,600
Borrowing (repayment) of short-term borrowings, net	614,700	0	0
Issuance of long-term debt, net of discounts	1,190,500	0	492,600
Debt financing costs		0	(9,800)
Repayment of long-term debt	(87,100)	(300)	(100)
Issuance of common stock	471,400	22,000	20,700
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	(18,100)	(1,700)	(15,800)
Cash provided by (used in) financing activities	(1,158,700)	(560,700)	(17,000)
Change in cash and cash equivalents	(211,300)	156,100	(37,800)
Change in cash and cash equivalents included in discontinued operations		(100)
Change in cash and cash equivalents included in continuing operations		156,000
Cash and cash equivalents at beginning of period	248,500	92,500	130,300
Cash and cash equivalents at end of period	37,200	248,500	92,500
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Operating activities
Cash provided by operating activities	1,348,300	1,334,500	1,196,700
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	0		0
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	0	0
Financing activities
Dividends paid	(1,332,000)	(1,332,000)	(1,230,500)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	2,001,200	(470,800)	(1,295,100)
Borrowing (repayment) of short-term borrowings, net	(1,110,300)	563,900	(509,000)
Issuance of long-term debt, net of discounts	0	1,000,000	798,900
Debt financing costs		(2,800)	(7,700)
Repayment of long-term debt	(900,000)	(1,100,000)	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			1,025,700
Contribution from general partner			21,000
Other	(7,200)	7,200	0
Cash provided by (used in) financing activities	(1,348,300)	(1,334,500)	(1,196,700)
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Reportable Legal Entities | Guarantor Subsidiary
Operating activities
Cash provided by operating activities	59,000	70,000	66,900
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	(83,000)		0
Other investing activities	(14,800)	(34,900)	(24,100)
Cash provided by (used in) investing activities	(68,200)	34,900	24,100
Financing activities
Dividends paid	(1,332,000)	(1,332,000)	(1,230,500)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	1,340,800	1,222,400	1,102,100
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	0	0	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	0	0	0
Cash provided by (used in) financing activities	8,800	(109,600)	(128,400)
Change in cash and cash equivalents	(400)	(4,700)	(37,400)
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		(4,700)
Cash and cash equivalents at beginning of period	400	5,100	42,500
Cash and cash equivalents at end of period	0	400	5,100
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Operating activities
Cash provided by operating activities	1,353,700	1,353,900	1,045,700
Investing activities
Capital expenditures	(512,400)	(624,400)	(1,188,200)
Contributions to unconsolidated affiliates	(4,900)		(27,500)
Other investing activities	(17,900)	25,700	(1,000)
Cash provided by (used in) investing activities	(499,400)	(650,100)	(1,214,700)
Financing activities
Dividends paid	0	0	0
Distributions to noncontrolling interests	(5,300)	(7,500)	(11,700)
Intercompany borrowings (advances), net	(841,300)	(688,500)	188,400
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	(7,700)	(7,700)	(7,700)
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	0	(100)	0
Cash provided by (used in) financing activities	(854,300)	(703,800)	169,000
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Reportable Legal Entities | Total
Operating activities
Cash provided by operating activities	1,315,400	1,353,300	1,022,800
Investing activities
Capital expenditures	(512,400)	(624,600)	(1,188,300)
Contributions to unconsolidated affiliates	(87,900)		(27,500)
Other investing activities	(32,700)	(9,200)	(25,100)
Cash provided by (used in) investing activities	(567,600)	(615,400)	(1,190,700)
Financing activities
Dividends paid	(829,400)	(517,600)	(509,200)
Distributions to noncontrolling interests	(276,300)	(549,400)	(535,900)
Intercompany borrowings (advances), net	0	0	0
Borrowing (repayment) of short-term borrowings, net	(495,600)	563,900	(509,000)
Issuance of long-term debt, net of discounts	1,190,500	1,000,000	1,291,500
Debt financing costs		(2,800)	(17,500)
Repayment of long-term debt	(994,800)	(1,108,000)	(7,800)
Issuance of common stock	471,400	22,000	20,700
Issuance of common units, net of issuance costs			375,700
Contribution from general partner			0
Other	(25,300)	5,400	(15,800)
Cash provided by (used in) financing activities	(959,500)	(586,500)	92,700
Change in cash and cash equivalents	(211,700)	151,400	(75,200)
Change in cash and cash equivalents included in discontinued operations		(100)
Change in cash and cash equivalents included in continuing operations		151,300
Cash and cash equivalents at beginning of period	248,900	97,600	172,800
Cash and cash equivalents at end of period	37,200	248,900	97,600
Consolidating Entries
Operating activities
Cash provided by operating activities	(2,393,000)	(2,122,100)	(1,936,800)
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	0		671,000
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	0	671,000
Financing activities
Dividends paid	2,664,000	2,664,000	2,461,000
Distributions to noncontrolling interests	(271,000)	(541,900)	(524,200)
Intercompany borrowings (advances), net	0	0	0
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	0	0	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			(650,000)
Contribution from general partner			(21,000)
Other	0	0	0
Cash provided by (used in) financing activities	2,393,000	2,122,100	1,265,800
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	$ 0	$ 0	$ 0