Equity Change in Preferred Units (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019		Dec. 31, 2019		Dec. 31, 2018
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 35,395	$ 36,388	[1]	$ 37,666	[1]	$ 36,788	[1]
Distributions to partners	(2,630)	(1,514)
Units issued for cash	1,580
Stockholders' Equity, Other	9	(28)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	(919)	1,206
Net income (loss)	(907)	1,219	[1]	5,112		3,829
Series B Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	547	547		556		556
Distributions to partners	(18)	(18)
Units issued for cash	0
Stockholders' Equity, Other	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	9
Net income (loss)		9
Series A Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	943	943		958		958
Distributions to partners	(30)	(30)
Units issued for cash	0
Stockholders' Equity, Other	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	15
Net income (loss)		15
Series C Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	440	440		440		440
Distributions to partners	(8)	(8)
Units issued for cash	0
Stockholders' Equity, Other	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	8
Net income (loss)		8
Series D Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	434	434		434		434
Distributions to partners	(9)	(8)
Units issued for cash	0
Stockholders' Equity, Other	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	9
Net income (loss)		8
Series E Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	786			786
Distributions to partners	(15)
Units issued for cash	0
Stockholders' Equity, Other	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	15
Series F Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	499			0
Distributions to partners	0
Units issued for cash	494
Stockholders' Equity, Other	(1)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	6
Series G Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,099			0
Distributions to partners	0
Units issued for cash	1,086
Stockholders' Equity, Other	(2)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	15
Series A Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		2,364				2,388
Distributions to partners		(64)
Net income (loss)		40
Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	4,748	2,364	[1]	$ 3,174	[1]	$ 2,388	[1]
Distributions to partners	(80)	(64)
Units issued for cash	1,580
Stockholders' Equity, Other	(3)	0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	$ 77	$ 40

[1] *As adjusted. See Note 1.