Shareholders' Equity, Components of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ 21,930		$ 21,386		$ 24,566
Other comprehensive income (loss)	727		911		(892)
Purchase of Boardwalk Pipelines common units					(1,718)
Balance	19,181		21,930		21,386
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(68)	[1]	(880)		(26)
Other comprehensive income (loss) before reclassifications, after tax	680	[1]	873		(922)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	47	[1]	38		30
Other comprehensive income (loss)	727	[1]	911		(892)
Amounts attributable to noncontrolling interests	(78)	[1]	(99)		95
Purchase of Boardwalk Pipelines common units					(29)
Balance	581	[1]	(68)	[1]	(880)
Net Unrealized Gains (Losses) on Investments with OTTI Losses [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	13		14		22
Other comprehensive income (loss) before reclassifications, after tax	(43)	[1]	(13)		(7)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	43	[1]	12		(7)
Other comprehensive income (loss)	0	[1]	(1)		(14)
Amounts attributable to noncontrolling interests					2
Balance	0	[1]	13		14
Cumulative effect adjustment from changes in accounting standards, tax					0
Other comprehensive income (loss) before reclassifications, tax	12		3		2
Reclassification of (gains) losses from accumulated other comprehensive loss, tax	(12)		(3)		2
Net Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	905		57		673
Other comprehensive income (loss) before reclassifications, after tax	763	[1]	957		(801)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	(43)	[1]	(8)		3
Other comprehensive income (loss)	720	[1]	949		(798)
Amounts attributable to noncontrolling interests	(75)	[1]	(101)		84
Balance	1,563	[1]	905		57
Cumulative effect adjustment from changes in accounting standards, tax					8
Other comprehensive income (loss) before reclassifications, tax	(201)		(256)		213
Reclassification of (gains) losses from accumulated other comprehensive loss, tax	12		1		(2)
Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(6)	[1]	5		0
Other comprehensive income (loss) before reclassifications, after tax	(22)	[1]	(11)		4
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	5	[1]			2
Other comprehensive income (loss)	(17)	[1]	(11)		6
Purchase of Boardwalk Pipelines common units					(1)
Balance	(23)	[1]	(6)	[1]	5
Cumulative effect adjustment from changes in accounting standards, tax					0
Other comprehensive income (loss) before reclassifications, tax	8		5		(2)
Reclassification of (gains) losses from accumulated other comprehensive loss, tax	(2)		0		0
Pension and Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(855)	[1]	(793)		(633)
Other comprehensive income (loss) before reclassifications, after tax	(66)	[1]	(102)		(34)
Reclassification of (gains) losses from accumulated other comprehensive loss, after tax	42	[1]	34		32
Other comprehensive income (loss)	(24)	[1]	(68)		(2)
Amounts attributable to noncontrolling interests	2	[1]	6
Purchase of Boardwalk Pipelines common units					(28)
Balance	(877)	[1]	(855)	[1]	(793)
Cumulative effect adjustment from changes in accounting standards, tax					0
Other comprehensive income (loss) before reclassifications, tax	18		28		9
Reclassification of (gains) losses from accumulated other comprehensive loss, tax	(11)		(9)		(6)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(125)	[1]	(163)		(88)
Other comprehensive income (loss) before reclassifications, after tax	48	[1]	42		(84)
Other comprehensive income (loss)	48	[1]	42		(84)
Amounts attributable to noncontrolling interests	(5)	[1]	(4)		9
Balance	(82)	[1]	(125)	[1]	(163)
Cumulative effect adjustment from changes in accounting standards, tax					0
Other comprehensive income (loss) before reclassifications, tax	0		0		0
Reclassification of (gains) losses from accumulated other comprehensive loss, tax	0		0		0
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	21,925				24,475
Balance			21,925
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			(28)
Balance					(28)
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Net Unrealized Gains (Losses) on Investments with OTTI Losses [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	0	[1]	4
Balance			0	[1]	4
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Net Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	918	[1]	98
Balance			918	[1]	98
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] | Pension and Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			(130)
Balance					(130)
Cumulative Effect, Period of Adoption, Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ (5)				(91)
Balance			(5)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			(54)
Balance					(54)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Net Unrealized Gains (Losses) on Investments with OTTI Losses [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			26
Balance					26
Cumulative Effect, Period of Adoption, Adjustment [Member] | Net Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			771
Balance					771
Cumulative Effect, Period of Adoption, Adjustment [Member] | Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			0
Balance					0
Cumulative Effect, Period of Adoption, Adjustment [Member] | Pension and Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			(763)
Balance					(763)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			$ (88)
Balance					$ (88)

[1] On January 1, 2020, the Company adopted ASU 2016-13; see Note 1. The Net Unrealized Gains (Losses) on Investments with OTTI Losses column that tracked the change in unrealized gains (losses) on investments with OTTI losses has been replaced with the Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses column. The balance as of January 1, 2020 in the Net Unrealized Gains (Losses) on Investments with OTTI Losses column is now reported in the Net Unrealized Gains (Losses) on Other Investments column. Prior period amounts were not adjusted for the adoption of this standard.