Pension and Postretirement Benefit Plans and Defined Contribution Plans - Narrative (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Retirement Benefits [Abstract] | |||
| Defined contribution plan, cost recognized | $ 622 | $ 380 | $ 317 |