Accounting Policies - Remaining Performance Obligations (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 $ in Billions	Sep. 30, 2019 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, amount	$ 20.6
Remaining performance obligation percentage expected to be recognized	26.00%
Performance obligation period	12 months