Reportable Segments and Revenue Recognition (Remaining Performance Obligation) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Revenue, remaining performance obligation, amount	$ 76	$ 82
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	76	$ 82
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Leases [Abstract]
Revenue, remaining performance obligation, amount	51
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 51
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months