Fair Value Measurements (Narrative) (Details) $ in Millions |
Sep. 30, 2017
USD ($)
|
---|---|
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract] | |
Asset value transferred into Level 1, as measured from the beginning of the reporting period | $ 110 |
Liability value transferred into Level 1, as measured from the beginning of the reporting period | $ 112 |