Callaway Energy Center (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) mill	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingencies [Line Items]
Nwf Fee Number Of Mills | mill	1
Former Gain Contingency, Recognized in Current Period	$ 24	$ 14	$ 15
Nuclear Plant
Loss Contingencies [Line Items]
Annual decommissioning costs included in costs of service	$ 7