Employee Benefit Plans (Rollforward of Level 3 Plan Assets) (Details) - Pension Plans - USD ($) $ in Millions |
12 Months Ended | |
---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
Pension and Other Postretirement Plans | ||
Fair value of plan assets at beginning of year | $ 3,431 | $ 3,497 |
Fair value of plan assets at end of year | 3,468 | 3,431 |
Level 3 | ||
Pension and Other Postretirement Plans | ||
Fair value of plan assets at beginning of year | 38 | 35 |
Actual return on plan assets related to assets held at end of period | 1 | 0 |
Purchases, sales, other settlements and issuances, net | 8 | 3 |
Fair value of plan assets at end of year | $ 47 | $ 38 |