Common Equity - Common Stock Dividends (Details) - $ / shares	1 Months Ended	3 Months Ended				12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends Paid and Payable [Line Items]
Common Stock, Dividends, Per Share, Declared		$ 0.4950	$ 0.4950	$ 0.4950	$ 0.4950	$ 1.98	$ 1.74	$ 1.56
Subsequent event
Dividends Paid and Payable [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.52
Annualized dividend	$ 2.08
Minimum | Subsequent event
Dividends Paid and Payable [Line Items]
Target dividend payout ratio (as a percent)	65.00%
Maximum | Subsequent event
Dividends Paid and Payable [Line Items]
Target dividend payout ratio (as a percent)	70.00%