Derivative Instruments Long-term debt (Details) $ in Millions	Sep. 30, 2017 USD ($)
Debt Disclosure in Derivatives Footnote [Abstract]
Long-term Debt, Percentage Bearing Variable Interest, Amount	$ 35
Long-term Debt, Percentage Bearing Fixed Interest, Amount	$ 200

The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

No definition available.

Name:	us-gaap_LongtermDebtPercentageBearingVariableInterestAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant