Pension and Other Postretirement Benefits - Expenses (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2020 |
Mar. 31, 2019 |
|
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||
| Net periodic benefit cost | $ 26 | |
| Multiemployer contribution | $ 28 | |
| Pension benefits | ||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||
| Net periodic benefit cost | 21 | 1 |
| Multiemployer contribution | 0 | 16 |
| Cost allocation | (1) | 5 |
| Pension and other postretirement benefits cost | 20 | 22 |
| Other postretirement benefits | ||
| Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] | ||
| Net periodic benefit cost | 6 | 0 |
| Multiemployer contribution | 0 | 5 |
| Cost allocation | 0 | 1 |
| Pension and other postretirement benefits cost | $ 6 | $ 6 |