Other Comprehensive Income (Loss) - Changes in AOCI Balance by Component (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Other Comprehensive Income (Loss)
Income Before Reclassifications		$ 73
Amounts Reclassified to Net Earnings		14
Tax (Expense) Benefit		(19)
Total Other Comprehensive Income (Loss)		68	$ 3
Pension and Other Post-Employment Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax		(598)
Other Comprehensive Income (Loss)
Income Before Reclassifications		0
Amounts Reclassified to Net Earnings		17
Tax (Expense) Benefit		(3)
Total Other Comprehensive Income (Loss)		14
Balance March 31, 2021, Net of Tax		(584)
Interest Rate Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax		62
Other Comprehensive Income (Loss)
Income Before Reclassifications		73
Amounts Reclassified to Net Earnings		0
Tax (Expense) Benefit		(17)
Total Other Comprehensive Income (Loss)		56
Balance March 31, 2021, Net of Tax		118
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax		(62)
Other Comprehensive Income (Loss)
Income Before Reclassifications		0
Amounts Reclassified to Net Earnings		(3)
Tax (Expense) Benefit		1
Total Other Comprehensive Income (Loss)		(2)
Balance March 31, 2021, Net of Tax		(64)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax		(598)
Other Comprehensive Income (Loss)
Total Other Comprehensive Income (Loss)	[1]	68	$ 3
Balance March 31, 2021, Net of Tax		$ (530)

[1] Accumulated Other Comprehensive Loss balances shown above are net of tax. The associated taxes were $137 million and $183 million as of March 31, 2021 and March 31, 2020, respectively. For additional information, see Note 11, Other Comprehensive Income.