Revenue Recognition - Remaining Performance Obligations (Details) $ in Millions	Jun. 30, 2020 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 4,728
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 933
Remaining performance obligation, expected timing of satisfaction, period	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 1,312
Remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 2,483
Remaining performance obligation, expected timing of satisfaction, period
Nuclear Operations Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 3,914
Nuclear Operations Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 722
Remaining performance obligation, expected timing of satisfaction, period	6 months
Nuclear Operations Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 1,098
Remaining performance obligation, expected timing of satisfaction, period	1 year
Nuclear Operations Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 2,094
Remaining performance obligation, expected timing of satisfaction, period
Nuclear Power Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 771
Nuclear Power Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 178
Remaining performance obligation, expected timing of satisfaction, period	6 months
Nuclear Power Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 209
Remaining performance obligation, expected timing of satisfaction, period	1 year
Nuclear Power Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 384
Remaining performance obligation, expected timing of satisfaction, period
Nuclear Services Group
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 43
Nuclear Services Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 33
Remaining performance obligation, expected timing of satisfaction, period	6 months
Nuclear Services Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 5
Remaining performance obligation, expected timing of satisfaction, period	1 year
Nuclear Services Group | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Total Remaining Performance Obligations	$ 5
Remaining performance obligation, expected timing of satisfaction, period