Pension and Postretirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gains and losses, Percent amortized	10.00%
Maximum employee contribution of eligible pay, Percent	75.00%
Semi-annual discretionary company contribution target, Percent	2.00%
Total expense related to participants in the Savings Plan	$ 178	$ 101	$ 99
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	50.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	42.00%
Other Types of Investments
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	8.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Minimum participant contribution to Savings Plan to be eligible for Success Share, Percent	1.00%
Semi-annual discretionary company contribution, Percent	0.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Company match of participant's contributions of eligible pay, Percent	5.00%
Semi-annual discretionary company contribution, Percent	6.00%
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$ 9	(6)
Actual return on plan assets	$ 0	0
Fair value of plan assets		0	0
Health care cost trend rate, percentage	7.00%
Health care cost trend rate, ultimate, percentage	5.00%
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$ 167	$ (267)
Weighted-average actual return on plan assets	(4.00%)	18.00%
Actual return on plan assets	$ (122)	$ 399
Fair value of plan assets	2,377	2,751	2,274
Accumulated benefit obligations	2,466	2,743
Expected future employer contributions next fiscal year	60
Pension Benefits | United States | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	421	589
Pension Benefits | Int’l.
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	165	5
Actual return on plan assets	(29)	71
Fair value of plan assets	902	972	$ 796
Accumulated benefit obligations	878	1,006
Expected future employer contributions next fiscal year	30
Pension Benefits | Int’l. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Pension Benefits | United States | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Level 3 | Pension Benefits | Int’l.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	14
Level 3 | Pension Benefits | Int’l. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0