Fair Value of Financial Instruments Fair Value Options Quantitative Disclosure (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Low [Member]
Commodity Contracts
Electricity physical forwards	$ 11.57	$ 14.60
Natural gas financial swaps	1.23	0.95
Financial swaps - electricity	15.50
High [Member]
Commodity Contracts
Electricity physical forwards	64.41	69.00
Natural gas financial swaps	3.74	4.64
Financial swaps - electricity	53.97
Weighted Average [Member]
Commodity Contracts
Electricity physical forwards	42.98	45.00
Natural gas financial swaps	1.69	1.82
Financial swaps - electricity	36.90
Assets [Member]
Commodity Contracts
Electricity physical forwards	0	3,000,000
Natural gas financial swaps	1,000,000	0
Financial swaps - electricity	1,000,000
Total commodity contracts	2,000,000	3,000,000
Liabilities [Member]
Commodity Contracts
Electricity physical forwards	96,000,000	84,000,000
Natural gas financial swaps	4,000,000	7,000,000
Financial swaps - electricity	3,000,000
Total commodity contracts	$ 103,000,000	$ 91,000,000