Acquisitions - Acquisition from Related Parties (Details) - Affiliated Entity - National Gas & Electric, LLC - Asset Purchase Agreement kWh in Thousands, $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($) usd_per_rce kWh state market	Mar. 31, 2018 kWh	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) kWh
Business Acquisition [Line Items]
Residential customer equivalent (in kwh) | kWh	50	50		35
Purchase price per RCE (in dollars per RCE) | usd_per_rce	250
Purchase price	$ 12.5
Number of markets | market	24
Number of states | state	8
Due to related parties				$ 8.8
Assets at date of transfer				1.7
Net distribution to NG&E recorded in equity			$ 0.1	$ 7.1