Pending Acquisition of Orbital ATK (Details) $ / shares in Units, $ in Billions	6 Months Ended
	Mar. 31, 2018 USD ($) $ / shares
Business Combinations [Abstract]
Payments to Acquire Businesses, Gross	$ 7.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	$ 1.4
Business Acquisition, Share Price | $ / shares	$ 134.50