Pension and Other Postretirement Benefit Plans (Fair Value of Plan Assets by Category) (Details) - USD ($) | Dec. 31, 2019 | Dec. 31, 2018 |
Significant unobservable inputs (Level 3) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 66,000,000 | $ 86,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3,527,000,000 | 3,194,000,000 |
Net asset value of plan assets | 973,000,000 | 969,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 24,000,000 | 10,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Government and government agency securities, U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 488,000,000 | 761,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Government and government agency securities, international securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 97,000,000 | 97,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Corporate bonds and notes, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1,389,000,000 | 860,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Corporate bonds and notes, international companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 277,000,000 | 155,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Equity securities, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 18,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Equity Securities, International Companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 51,000,000 | 185,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 128,000,000 | 35,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Funds, U.S. equity securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 367,000,000 | 501,000,000 |
Net asset value of plan assets | 367,000,000 | 501,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Funds, International equity securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 215,000,000 | 52,000,000 |
Net asset value of plan assets | 215,000,000 | 52,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Funds, Short-term investment fund | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 15,000,000 | 102,000,000 |
Net asset value of plan assets | 15,000,000 | 102,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Funds, International debt securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 251,000,000 | 209,000,000 |
Net asset value of plan assets | 251,000,000 | 209,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Fund of Funds, International equity securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 59,000,000 | 50,000,000 |
Net asset value of plan assets | 59,000,000 | 50,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Common and Collective Funds, Real estate | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 34,000,000 | 36,000,000 |
Net asset value of plan assets | 34,000,000 | 36,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Limited partnerships, U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 53,000,000 | 68,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Limited partnerships, diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 5,000,000 | 6,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Limited partnerships, emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8,000,000 | 12,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 66,000,000 | 37,000,000 |
Net asset value of plan assets | 32,000,000 | 19,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 51,000,000 | 238,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Government and government agency securities, U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Government and government agency securities, international securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Corporate bonds and notes, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Corporate bonds and notes, international companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Equity securities, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 18,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Equity Securities, International Companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 51,000,000 | 185,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 35,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Limited partnerships, U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Limited partnerships, diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | Limited partnerships, emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Quoted prices (Level 1) | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 2,437,000,000 | 1,901,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 24,000,000 | 10,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Government and government agency securities, U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 488,000,000 | 761,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Government and government agency securities, international securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 97,000,000 | 97,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Corporate bonds and notes, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1,389,000,000 | 860,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Corporate bonds and notes, international companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 277,000,000 | 155,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Equity securities, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Equity Securities, International Companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 128,000,000 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Limited partnerships, U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Limited partnerships, diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | Limited partnerships, emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Other significant observable inputs (Level 2) | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 34,000,000 | 18,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 66,000,000 | 86,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Government and government agency securities, U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Government and government agency securities, international securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Corporate bonds and notes, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Corporate bonds and notes, international companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Equity securities, U.S. companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Equity Securities, International Companies | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Limited partnerships, U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 53,000,000 | 68,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Limited partnerships, diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 5,000,000 | 6,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | Limited partnerships, emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 8,000,000 | 12,000,000 |
Fair Value, Measurements, Recurring | Pension Benefits | Significant unobservable inputs (Level 3) | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 0 | $ 0 |