Borrowings and Other Financing Instruments Forward Equity Agreement (Details) - Forward Equity Agreements [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Jun. 30, 2020	Nov. 04, 2019
Forward Contract Indexed to Issuer's Equity [Line Items]
Common Stock, Value, to be Issued through Forward Equity Agreement		$ 743
Common Stock, Shares to be Issued through forward Equity Agreement		11.8
Common shares, price per share used in forward calculation		$ 62.69
Common stock, interest rate spread used in forward calculation		0.75%
Period End Settlement Price, In Shares		11.8
Period End Settlement Price, in Cash		$ 728
Period End Net Cash Settlement Price		$ 24
Period End Net Share Settlement Price		0.4
Common stock, initial shares in an agreement		10.3
Common stock, additional shares in an agreement		1.5
Minimum [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Expected settlement price	$ 720
Maximum [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Expected settlement price	$ 730