Balance Sheets (Unaudited) - MEC (Parenthetical) - $ / shares shares in Millions	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, shares authorized	100	100
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares issued	2	4
Preferred stock, shares outstanding	2	4
Common stock, shares authorized	115	115
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares issued	76	76
Common stock, shares outstanding	76	76
MEC
Common stock, shares authorized	350	350
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares issued	71	71
Common stock, shares outstanding	71	71