Employee Pension and Other Postretirement Benefits - Pension and Post retirement Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan and Other Postretirement Benefits Plan
Amortization period of net actuarial losses		8 years
Assetsmoothingperiodofnonamortizing amount		4 years
Pension and Executive Employee Supplemental Benefit, Pension Plan [Member]
Pension Plan and Other Postretirement Benefits Plan
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax		$ 942	$ 793
Defined Benefit Plan, Accumulated Other Comprehensive Income, Tax		248	209
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax		694	584
Pension Benefits
Pension Plan and Other Postretirement Benefits Plan
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax		910	753
Defined Benefit Plan, Service Cost		80	71	$ 91
2018		140
2019		147
2020		153
2021		160
2022		166
Years 2023-2027		914
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year		(62)
Defined Benefit Plan, Interest Cost		100	100	103
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(268)	(254)	(235)
Amortization of prior service credit		(26)	(27)	(18)
Defined Benefit Plan, Amortization of Gain (Loss)		87	79	75
Curtailment gain		0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		(27)	(31)	16
Defined Benefit Plan, Accumulated Other Comprehensive Income, Tax		240	198
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax		670	555
Domestic Plan [Member]
Pension Plan and Other Postretirement Benefits Plan
2018		17
2019		17
2020		18
2021		18
2022		18
Years 2023-2027		82
Other Benefits
Pension Plan and Other Postretirement Benefits Plan
Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax		50	22
Defined Benefit Plan, Service Cost		4	6	8
Defined Benefit Plan, Interest Cost		8	8	9
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		(21)	(19)	(19)
Amortization of prior service credit		(15)	(21)	(12)
Defined Benefit Plan, Amortization of Gain (Loss)		5	8	10
Curtailment gain		0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		(19)	(18)	(4)
Defined Benefit Plan, Accumulated Other Comprehensive Income, Tax		14	6
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax		36	16
Superannuation Supplemental Executives Retirement Plan Defined Benefit and Executive Supplemental Defined Benefit Plan [Member]
Pension Plan and Other Postretirement Benefits Plan
Defined Benefit Plan, Service Cost		0	0	2
Defined Benefit Plan, Interest Cost		3	3	2
Defined Benefit Plan, Expected Return (Loss) on Plan Assets		0	0	0
Amortization of prior service credit		0	0	0
Defined Benefit Plan, Amortization of Gain (Loss)		3	4	3
Curtailment gain		0	0	(2)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		$ 6	$ 7	$ 5
Forecast | Pension Benefits
Pension Plan and Other Postretirement Benefits Plan
Effect of 50 basis point increase on discount rate	$ 25
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 27