Postretirement Benefit Plans (Fair Value of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 691	$ 605
Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	43	488
Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	188	35
Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	384	13
NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	76	69
Global stock funds/securities
Defined Benefit Plan Disclosure
Fair value of plan assets	118	103
Global stock funds/securities | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	38	90
Global stock funds/securities | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	66	0
Global stock funds/securities | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Global stock funds/securities | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	14	13
Diversified growth and income funds
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 26	$ 9
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember
Diversified growth and income funds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 26	$ 9
Corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	105	91
Corporate bonds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	1	86
Corporate bonds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	97	0
Corporate bonds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Corporate bonds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	7	5
Government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	47	62
Government bonds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	0	35
Government bonds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	19	0
Government bonds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Government bonds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	28	27
Hedging instruments
Defined Benefit Plan Disclosure
Fair value of plan assets	6	39
Hedging instruments | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	0	4
Hedging instruments | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	6	35
Hedge funds
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 1	$ 12
Defined Benefit Plan, Plan Assets, Fair Value by Hierarchy and NAV [Extensible List]	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember	us-gaap:FairValueMeasuredAtNetAssetValuePerShareMember
Hedge funds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 1	$ 12
Insurance contracts and other
Defined Benefit Plan Disclosure
Fair value of plan assets	384	16
Insurance contracts and other | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets
Insurance contracts and other | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Insurance contracts and other | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	384	13
Insurance contracts and other | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets		3
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	4	273
Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	4	273
Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Cash and cash equivalents | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0	$ 0