Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Forward Equity Agreement (Details) - Forward Equity Agreements [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Jun. 30, 2019	Nov. 30, 2018
Forward Contract Indexed to Issuer's Equity [Line Items]
Common Stock, Value, to be Issued through Forward Equity Agreement		$ 459
Common Stock, Shares to be Issued through forward Equity Agreement		9.4
Common stock, initial shares in an agreement		8.1
Common stock, additional shares in an agreement		1.2
Period End Settlement Price, In Shares	9.4
Period End Settlement Price, in Cash	$ 452
Period End Net Cash Settlement Price	$ 100
Period End Net Share Settlement Price	1.7
Common shares, price per share used in forward calculation		$ 49.00
Common stock, interest rate spread used in forward calculation		0.75%
expected settlement price	$ 450