Defined Benefit Pension And Other Postretirement Plans (Summary Of Projected Benefit Obligations And Funded Status For Defined Benefit Pension And Other Postretirement Plans) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Change in plan assets:
Fair value of plan assets at January 1		$ 1,840
Fair value of plan assets at December 31		2,089		$ 1,840
Amounts recognized in the consolidated balance sheets:
Noncurrent liabilities		(1,509)		(1,099)
Pension Benefits
Change in benefit obligations:
Benefit obligations at January 1		2,164		2,024
Service cost		159		132	$ 114
Interest cost		83		75	73
Actuarial (gain) loss		(159)		150
Benefits paid		(273)		(217)
Plan amendments		(90)		0
Acquisitions		895		0
Benefit obligations at December 31		2,779		2,164	2,024
Change in plan assets:
Fair value of plan assets at January 1		1,840		1,659
Actual return on plan assets		(115)		270
Employer contributions		115		128
Benefits paid from plan assets		(273)		(217)
Acquisitions		522		0
Fair value of plan assets at December 31		2,089		1,840	1,659
Funded status of plans at December 31		(690)		(324)
Amounts recognized in the consolidated balance sheets:
Current liabilities		(21)		(18)
Noncurrent liabilities		(669)		(306)
Accrued benefit cost		(690)		(324)
Pretax amounts recognized in accumulated other comprehensive loss:
Net actuarial loss		517	[1]	537
Prior service cost (credit)		(295)	[1]	(238)
Pension Benefits | LOOP LLC and Explorer Pipeline
Pretax amounts recognized in accumulated other comprehensive loss:
Net actuarial loss	[1]	18
Other Benefits
Change in benefit obligations:
Benefit obligations at January 1		826		740
Service cost		30		25	32
Interest cost		30		30	35
Actuarial (gain) loss		(71)		61
Benefits paid		(36)		(30)
Plan amendments		34		0
Acquisitions		71		0
Benefit obligations at December 31		884		826	740
Change in plan assets:
Fair value of plan assets at January 1		0		0
Actual return on plan assets		0		0
Employer contributions		36		30
Benefits paid from plan assets		(36)		(30)
Acquisitions		0		0
Fair value of plan assets at December 31		0		0	$ 0
Funded status of plans at December 31		(884)		(826)
Amounts recognized in the consolidated balance sheets:
Current liabilities		(44)		(33)
Noncurrent liabilities		(840)		(793)
Accrued benefit cost		(884)		(826)
Pretax amounts recognized in accumulated other comprehensive loss:
Net actuarial loss		9	[1]	80
Prior service cost (credit)		35	[1]	$ (3)
Other Benefits | LOOP LLC and Explorer Pipeline
Pretax amounts recognized in accumulated other comprehensive loss:
Net actuarial loss	[1]	$ 1

[1] Amounts exclude those related to LOOP and Explorer, equity method investees with defined benefit pension and postretirement plans for which net losses of $18 million and less than $1 million were recorded in accumulated other comprehensive loss in 2018, reflecting our ownership share.