Fair Value Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - Fair Value, Measurements, Recurring [Member] $ in Millions	9 Months Ended
	Jun. 30, 2017 USD ($)
Fair Value, Assets [Roll Forward]
Auction rate securities Beginning Balance	$ 2.3
Auction rate securities Ending Balance	0.0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets [Roll Forward]
Auction rate securities Beginning Balance	2.3
Auction rate securities Ending Balance	0.0
Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member]
Fair Value, Assets [Roll Forward]
Auction rate securities Beginning Balance	2.3
Decreases in Level 3 assets	(2.3)
Auction rate securities Ending Balance	$ 0.0