Postretirement Benefit Plans (Fair Value of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 605	$ 567
NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	69	271
Global stock funds/securities | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	13	29
Index funds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	0	1
Corporate bonds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	5	25
Government bonds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	27	20
Hedge funds | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	12	67
Insurance contracts and other | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	3
Cash and cash equivalents | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets	0
Estimate of Fair Value Measurement
Defined Benefit Plan Disclosure
Fair value of plan assets	605	567
Estimate of Fair Value Measurement | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	488	262
Estimate of Fair Value Measurement | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	35	22
Estimate of Fair Value Measurement | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	13	12
Estimate of Fair Value Measurement | Global stock funds/securities
Defined Benefit Plan Disclosure
Fair value of plan assets	103	117
Estimate of Fair Value Measurement | Global stock funds/securities | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	90	88
Estimate of Fair Value Measurement | Global stock funds/securities | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Global stock funds/securities | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Index funds
Defined Benefit Plan Disclosure
Fair value of plan assets	0	1
Estimate of Fair Value Measurement | Index funds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Index funds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Index funds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	91	59
Estimate of Fair Value Measurement | Corporate bonds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	86	34
Estimate of Fair Value Measurement | Corporate bonds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Corporate bonds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Government bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	62	51
Estimate of Fair Value Measurement | Government bonds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	35	31
Estimate of Fair Value Measurement | Government bonds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Government bonds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Hedging Instruments
Defined Benefit Plan Disclosure
Fair value of plan assets	39	27
Estimate of Fair Value Measurement | Hedging Instruments | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	4	5
Estimate of Fair Value Measurement | Hedging Instruments | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	35	22
Estimate of Fair Value Measurement | Hedge funds
Defined Benefit Plan Disclosure
Fair value of plan assets	12	67
Estimate of Fair Value Measurement | Hedge funds | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Hedge funds | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Hedge funds | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Insurance contracts and other
Defined Benefit Plan Disclosure
Fair value of plan assets	16	186
Estimate of Fair Value Measurement | Insurance contracts and other | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets		104
Estimate of Fair Value Measurement | Insurance contracts and other | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Insurance contracts and other | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	13	12
Estimate of Fair Value Measurement | Insurance contracts and other | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets		70
Estimate of Fair Value Measurement | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	273	0
Estimate of Fair Value Measurement | Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure
Fair value of plan assets	273	0
Estimate of Fair Value Measurement | Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Estimate of Fair Value Measurement | Cash and cash equivalents | Level 3
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0	0
Estimate of Fair Value Measurement | Cash and cash equivalents | NAV Practical Expedient
Defined Benefit Plan Disclosure
Fair value of plan assets		$ 0