Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unaudited Quarterly Financial Data [Line Items]
Total revenues									$ 2,471,406	$ 2,425,800	$ 2,744,965
Operating income									847,471	856,086	1,009,238
Income (loss) from continuing operations									628,381	4,479,586	907,621
Discontinued operations, net									0	518	397
Net income									628,381	4,480,104	908,018
Net income available to Common Shares									$ 600,363	$ 4,289,072	$ 863,277
Earnings per share – basic:
Net income available to Common Shares									$ 1.64	$ 11.75	$ 2.37
Weighted average Common Shares outstanding									366,968	365,002	363,498
Earnings per share – diluted:
Net income available to Common Shares									$ 1.63	$ 11.68	$ 2.36
Weighted average Common Shares outstanding									382,678	381,992	380,620
ERPOP [Member]
Unaudited Quarterly Financial Data [Line Items]
Total revenues									$ 2,471,406	$ 2,425,800	$ 2,744,965
Operating income									847,471	856,086	1,009,238
Income (loss) from continuing operations									628,381	4,479,586	907,621
Discontinued operations, net									0	518	397
Net income									628,381	4,480,104	908,018
Net income available to Units									$ 622,967	$ 4,460,583	$ 897,518
Earnings per share – basic:
Net income available to Common Shares									$ 1.64	$ 11.75	$ 2.37
Weighted average Units outstanding									379,869	378,829	377,074
Earnings per share – diluted:
Net income available to Common Shares									$ 1.63	$ 11.68	$ 2.36
Weighted average Common Shares outstanding									382,678	381,992	380,620
Scenario, Previously Reported [Member]
Unaudited Quarterly Financial Data [Line Items]
Total revenues	$ 630,704	$ 624,122	$ 612,480	$ 604,100	$ 605,489	$ 606,074	$ 595,154	$ 619,083
Operating income	214,764	217,786	210,550	204,371	224,070	209,373	206,018	216,625
Income (loss) from continuing operations	130,084	144,196	204,160	149,941	301,987	217,246	228,365	3,731,988
Discontinued operations, net					394	246	35	(157)
Net income	130,084	144,196	204,160	149,941	302,381	217,492	228,400	3,731,831
Net income available to Common Shares	$ 124,669	$ 137,457	$ 195,268	$ 142,969	$ 276,477	$ 207,543	$ 218,067	$ 3,586,985
Earnings per share – basic:
Net income available to Common Shares	$ 0.34	$ 0.37	$ 0.53	$ 0.39	$ 0.76	$ 0.57	$ 0.60	$ 9.84
Weighted average Common Shares outstanding	367,442	366,996	366,820	366,605	365,256	365,109	365,047	364,592
Earnings per share – diluted:
Net income available to Common Shares	$ 0.34	$ 0.37	$ 0.53	$ 0.39	$ 0.75	$ 0.56	$ 0.59	$ 9.76
Weighted average Common Shares outstanding	383,105	382,945	382,692	382,280	381,860	382,373	382,065	382,243
Scenario, Previously Reported [Member] | ERPOP [Member]
Unaudited Quarterly Financial Data [Line Items]
Total revenues	$ 630,704	$ 624,122	$ 612,480	$ 604,100	$ 605,489	$ 606,074	$ 595,154	$ 619,083
Operating income	214,764	217,786	210,550	204,371	224,070	209,373	206,018	216,625
Income (loss) from continuing operations	130,084	144,196	204,160	149,941	301,987	217,246	228,365	3,731,988
Discontinued operations, net					394	246	35	(157)
Net income	130,084	144,196	204,160	149,941	302,381	217,492	228,400	3,731,831
Net income available to Units	$ 129,342	$ 142,623	$ 202,622	$ 148,380	$ 287,546	$ 215,896	$ 226,847	$ 3,730,294
Earnings per share – basic:
Net income available to Common Shares	$ 0.34	$ 0.37	$ 0.53	$ 0.39	$ 0.76	$ 0.57	$ 0.60	$ 9.84
Weighted average Units outstanding	380,325	379,906	379,733	379,504	379,081	379,008	378,934	378,289
Earnings per share – diluted:
Net income available to Common Shares	$ 0.34	$ 0.37	$ 0.53	$ 0.39	$ 0.75	$ 0.56	$ 0.59	$ 9.76
Weighted average Units outstanding	383,105	382,945	382,692	382,280	381,860	382,373	382,065	382,243