Other Comprehensive Income (Loss) - Changes in AOCI balance by Component (Details) - USD ($) $ in Millions	3 Months Ended												9 Months Ended
	Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Sep. 30, 2020
Other Comprehensive Income (Loss)
Income (Loss) Before Reclassifications													$ 35
Amounts Reclassified to Net Earnings													41
Tax Expense													(19)
Total Other Comprehensive Income (Loss)	$ 34		$ 20		$ 3		$ 7		$ 4		$ 2		57
Pension and Other Post-Employment Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2019, Net of Tax					(619)								(619)
Other Comprehensive Income (Loss)
Income (Loss) Before Reclassifications													0
Amounts Reclassified to Net Earnings													38
Tax Expense													(9)
Total Other Comprehensive Income (Loss)													29
Balance September 30, 2020, Net of Tax	(590)												(590)
Interest Rate Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2019, Net of Tax					0								0
Other Comprehensive Income (Loss)
Income (Loss) Before Reclassifications													44
Amounts Reclassified to Net Earnings													0
Tax Expense													(10)
Total Other Comprehensive Income (Loss)													34
Balance September 30, 2020, Net of Tax	34												34
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2019, Net of Tax					(56)								(56)
Other Comprehensive Income (Loss)
Income (Loss) Before Reclassifications													(9)
Amounts Reclassified to Net Earnings													3
Tax Expense													0
Total Other Comprehensive Income (Loss)													(6)
Balance September 30, 2020, Net of Tax	(62)												(62)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2019, Net of Tax					(675)								(675)
Other Comprehensive Income (Loss)
Total Other Comprehensive Income (Loss)	34	[1]	$ 20	[1]	$ 3	[1]	$ 7	[2]	$ 4	[2]	$ 2	[2]
Balance September 30, 2020, Net of Tax	$ (618)												$ (618)

[1] Accumulated Other Comprehensive Loss balances shown above are net of tax. The associated taxes were $183 million, $178 million and $165 million as of first, second and third quarters 2020, respectively. For additional information, see Note 11, Other Comprehensive Income.

[2] Accumulated Other Comprehensive Loss balances shown above are net of tax. The associated taxes were $179 million, $177 million and $175 million as of first, second and third quarters 2019, respectively. For additional information, see Note 11, Other Comprehensive Income.