Accumulated Other Comprehensive Income (Loss) - Items Reclassified out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Loss [Abstract]
Defined Benefit Plans	$ 29	$ 30	$ 83	$ 46
Tax expense of defined benefit plans	$ 7	$ 7	$ 22	$ 11

Amount, after tax, of reclassification adjustment from accumulated other comprehensive (income) loss for net periodic benefit cost (credit) of defined benefit plan.

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Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration