Common Equity - Common Stock Dividends (Details) - $ / shares	3 Months Ended					12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dividends Paid and Payable [Line Items]
Dividends per share (in dollars per share)		$ 0.59	$ 0.59	$ 0.59	$ 0.59		$ 2.36	$ 2.21	$ 2.08
Subsequent event
Dividends Paid and Payable [Line Items]
Dividends per share (in dollars per share)	$ 0.6325
Annualized dividend (in dollars per share)						$ 2.53
Subsequent event | Minimum
Dividends Paid and Payable [Line Items]
Target dividend payout ratio (as a percent)						65.00%
Subsequent event | Maximum
Dividends Paid and Payable [Line Items]
Target dividend payout ratio (as a percent)						70.00%