Equity Change in Preferred Units (Details) - USD ($) $ in Millions	3 Months Ended							6 Months Ended			12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020		Jun. 30, 2019		Mar. 31, 2019		Jun. 30, 2020	Jun. 30, 2019		Dec. 31, 2019		Dec. 31, 2018
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 35,566	$ 35,105	[1]	$ 36,454	[1]	$ 36,388	[1]	$ 35,566	$ 36,454	[1]	$ 37,425	[1]	$ 36,788	[1]
Distributions to partners		(2,630)		(1,643)		(1,514)			(67)
Units issued for cash		1,580		780
Stockholders' Equity, Other	33	(18)		(37)		28
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	706	(926)		1,269		1,206
Net income (loss)	719			1,282	[1]			(195)	2,501	[1]	5,112		3,829
Series B Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	556	547		556		547		556	556		556		556
Distributions to partners	0	(18)		0		(18)
Units issued for cash		0		0
Stockholders' Equity, Other	0	0		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	9	9
Net income (loss)				9		9
Series A Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	958	943		958		943		958	958		958		958
Distributions to partners	0	(30)		0		(30)
Units issued for cash		0		0
Stockholders' Equity, Other	0	0		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	15	15
Net income (loss)				15		15
Series C Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	440	440		440		440		440	440		440		440
Distributions to partners	(8)	(8)		(9)		(8)
Units issued for cash		0		0
Stockholders' Equity, Other	0	0		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	8	8
Net income (loss)				9		8
Series D Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	434	434		434		434		434	434		434		434
Distributions to partners	(8)	(9)		(9)		(8)
Units issued for cash		0		0
Stockholders' Equity, Other	0	0		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	8	9
Net income (loss)				9		8
Series E Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	786	786		790		0		786	790		786		0
Distributions to partners	(15)	(15)		0		0
Units issued for cash		0		780
Stockholders' Equity, Other	0	0		(1)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	15	15
Net income (loss)				11		0
Series F Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	496	499						496			0
Distributions to partners	(11)	0
Units issued for cash		494
Stockholders' Equity, Other	(1)	(1)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	9	6
Series G Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,094	1,099						1,094			0
Distributions to partners	(25)	0
Units issued for cash		1,086
Stockholders' Equity, Other	0	(2)
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	20	15
Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	4,764	4,748	[1]	3,178	[1]	2,364	[1]	$ 4,764	$ 3,178	[1]	$ 3,174	[1]	$ 2,388	[1]
Distributions to partners	(67)	(80)		(18)		(64)
Units issued for cash		1,580		780
Stockholders' Equity, Other	(1)	(3)		(1)		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	$ 84	$ 77		53		40
Net income (loss)				$ 53		$ 40

[1] *As adjusted. See Note 1.