Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 21,902	$ 23,848	$ 21,386	$ 24,566
Cumulative effect adjustments from changes in accounting standards				(91)
Balance, as adjusted				24,475
Other comprehensive income (loss)	440	(199)	989	(606)
Purchase of Boardwalk Pipeline common units		(1,715)		(1,715)
Ending Balance	22,394	21,858	22,394	21,858
OTTI Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	18	18	14	22
Cumulative effect adjustments from changes in accounting standards				4
Balance, as adjusted				26
Other comprehensive income (loss) before reclassifications, after tax	(1)	(1)	3	(11)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	1		1	1
Other comprehensive income (loss)		(1)	4	(10)
Amounts attributable to noncontrolling interests				1
Ending Balance	18	17	18	17
Unrealized Gains (Losses) on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	527	386	57	673
Cumulative effect adjustments from changes in accounting standards				98
Balance, as adjusted				771
Other comprehensive income (loss) before reclassifications, after tax	434	(156)	955	(570)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	2	(3)	7	(18)
Other comprehensive income (loss)	436	(159)	962	(588)
Amounts attributable to noncontrolling interests	(46)	17	(102)	61
Ending Balance	917	244	917	244
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1)	10	5
Other comprehensive income (loss) before reclassifications, after tax	(6)	4	(12)	12
Reclassification of (gains) losses from accumulated other comprehensive income, after tax				2
Other comprehensive income (loss)	(6)	4	(12)	14
Purchase of Boardwalk Pipeline common units		(1)		(1)
Ending Balance	(7)	13	(7)	13
Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(786)	(753)	(793)	(633)
Cumulative effect adjustments from changes in accounting standards				(130)
Balance, as adjusted				(763)
Other comprehensive income (loss) before reclassifications, after tax			(1)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	7	9	16	19
Other comprehensive income (loss)	7	9	15	19
Amounts attributable to noncontrolling interests	(1)	(2)	(2)	(2)
Purchase of Boardwalk Pipeline common units		(28)		(28)
Ending Balance	(780)	(774)	(780)	(774)
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(148)	(78)	(163)	(88)
Balance, as adjusted				(88)
Other comprehensive income (loss) before reclassifications, after tax	3	(52)	20	(41)
Other comprehensive income (loss)	3	(52)	20	(41)
Amounts attributable to noncontrolling interests		5	(2)	4
Ending Balance	(145)	(125)	(145)	(125)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(390)	(417)	(880)	(26)
Cumulative effect adjustments from changes in accounting standards				(28)
Balance, as adjusted				(54)
Other comprehensive income (loss) before reclassifications, after tax	430	(205)	965	(610)
Reclassification of (gains) losses from accumulated other comprehensive income, after tax	10	6	24	4
Other comprehensive income (loss)	440	(199)	989	(606)
Amounts attributable to noncontrolling interests	(47)	20	(106)	64
Purchase of Boardwalk Pipeline common units		(29)		(29)
Ending Balance	$ 3	$ (625)	$ 3	$ (625)