Pension and Other Postretirement Benefit Plans (Fair Value of Plan Assets by Category) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015 |
Significant unobservable inputs (Level 3) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 132 | $ 156 |
Fair Value, Measurements, Recurring | Pension Plan | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 3,174 | 3,293 |
Net asset value of plan assets | 746 | 778 |
Fair Value, Measurements, Recurring | Pension Plan | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 47 | 26 |
Fair Value, Measurements, Recurring | Pension Plan | U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 455 | 494 |
Fair Value, Measurements, Recurring | Pension Plan | International securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 163 | 212 |
Fair Value, Measurements, Recurring | Pension Plan | Domestic Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 892 | 909 |
Fair Value, Measurements, Recurring | Pension Plan | Foreign Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 190 | 160 |
Fair Value, Measurements, Recurring | Pension Plan | U.S. Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 13 |
Fair Value, Measurements, Recurring | Pension Plan | Foreign Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 454 | 472 |
Fair Value, Measurements, Recurring | Pension Plan | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 64 | 59 |
Fair Value, Measurements, Recurring | Pension Plan | Common and Collective Funds, U.S. equity securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Net asset value of plan assets | 650 | 648 |
Fair Value, Measurements, Recurring | Pension Plan | Common and Collective Funds, International equity securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Net asset value of plan assets | 56 | 65 |
Fair Value, Measurements, Recurring | Pension Plan | Common and Collective Funds, Short-term investment fund | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Net asset value of plan assets | 30 | 55 |
Fair Value, Measurements, Recurring | Pension Plan | U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 104 | 120 |
Fair Value, Measurements, Recurring | Pension Plan | Diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 21 |
Fair Value, Measurements, Recurring | Pension Plan | Emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 15 |
Fair Value, Measurements, Recurring | Pension Plan | Real estate | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Net asset value of plan assets | 10 | 10 |
Fair Value, Measurements, Recurring | Pension Plan | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 17 | 14 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 579 | 570 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 47 | 26 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | International securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Domestic Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Foreign Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | U.S. Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 13 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Foreign Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 454 | 472 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 64 | 59 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Quoted prices (Level 1) | Emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | 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 Plan | Other significant observable inputs (Level 2) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 1,717 | 1,789 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Cash and cash equivalents | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 455 | 494 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | International securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 163 | 212 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Domestic Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 892 | 909 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Foreign Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 190 | 160 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | U.S. Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Foreign Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Mutual funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | Emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Other significant observable inputs (Level 2) | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 17 | 14 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 132 | 156 |
Fair Value, Measurements, Recurring | Pension Plan | 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 Plan | Significant unobservable inputs (Level 3) | U.S. securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | International securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | Domestic Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | Foreign Corporate Debt Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | U.S. Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | Foreign Equity Securities | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 0 | 0 |
Fair Value, Measurements, Recurring | Pension Plan | 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 Plan | Significant unobservable inputs (Level 3) | U.S. private equity investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 104 | 120 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | Diversified fund of funds | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 21 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | Emerging growth | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | 14 | 15 |
Fair Value, Measurements, Recurring | Pension Plan | Significant unobservable inputs (Level 3) | All other investments | | |
Defined Benefit Plan Disclosure [Line Items] | | |
Fair value of plan assets | $ 0 | $ 0 |