Equity Change in Preferred Units (Details) - USD ($) $ in Millions	3 Months Ended										9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Sep. 30, 2020	Sep. 30, 2019		Dec. 31, 2019		Dec. 31, 2018
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 33,717	$ 35,566	$ 35,105	[1]	$ 35,743		$ 36,454	[1]	$ 36,388	[1]	$ 33,717	$ 35,743		$ 37,425	[1]	$ 36,788	[1]
Distributions to partners	(1,180)	(67)	(2,630)		(1,644)		(1,643)		(1,514)
Units issued for cash			1,580				780
Stockholders' Equity, Other	3	33	(18)		4		(37)		28
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	(373)	706	(926)		1,238		1,269		1,206
Net income (loss)	(362)		5,112		1,250	[1]			3,829		(557)	3,751	[1]
Series B Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	547	556	547		547		556		547		547	547		556		556
Distributions to partners	(18)	0	(18)		(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	9
Net income (loss)					9		9		9
Series A Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	943	958	943		944		958		943		943	944		958		958
Distributions to partners	(30)	0	(30)		(29)		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	15
Net income (loss)					15		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		440		440
Distributions to partners	(8)	(8)	(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	8
Net income (loss)					8		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		434		434
Distributions to partners	(9)	(8)	(9)		(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	9	8	9
Net income (loss)					8		9		8
Series E Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	786	786	786		786		790		0		786	786		786		0
Distributions to partners	(15)	(15)	(15)		(19)		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	15
Net income (loss)					15		11		0
Series F Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	505	496	499								505			0
Distributions to partners	0	(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	9	6
Series G Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,113	1,094	1,099								1,113			0
Distributions to partners	0	(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	19	20	15
Preferred Units [Member]
Preferred Units [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	4,768	4,764	4,748	[1]	3,151		3,178	[1]	2,364	[1]	$ 4,768	$ 3,151		$ 3,174	[1]	$ 2,388	[1]
Distributions to partners	(80)	(67)	(80)		(82)		(18)		(64)
Units issued for cash			1,580				780
Stockholders' Equity, Other	0	(1)	(3)		0		(1)		0
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Redeemable Noncontrolling Interest	$ 84	$ 84	$ 77		55		53		40
Net income (loss)					$ 55		$ 53		$ 40

[1] *As adjusted. See Note 1.