Revenues (Tables)

6 Months Ended

Jun. 30, 2018

Revenue From Contract With Customer [Abstract]

Schedule of Change In Customer Advances Balance

The table below shows the change in the customer advances balance for the six months ended June 30, 2018 ($ in millions).

	Customer Advances Balance as of January 1, 2018		Cash Received in Advance of Satisfying Performance Obligation		Revenue Recognized		Customer Advances Balance as of June 30, 2018
Total	$	12.7	$	56.8	$	54.2	$	15.3