Balance Sheets (Unaudited) - MEC (Parenthetical) - $ / shares shares in Millions	Mar. 31, 2024	Dec. 31, 2023
Common stock, shares authorized (in shares)	115	115
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares issued (in shares)	76	76
Common stock, shares outstanding (in shares)	76	76
MEC
Common stock, shares authorized (in shares)	350	350
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares issued (in shares)	71	71
Common stock, shares outstanding (in shares)	71	71