CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) $ in Millions	Sep. 30, 2021 USD ($) shares	Sep. 30, 2021 SFr / shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2020 SFr / shares
CONDENSED CONSOLIDATED BALANCE SHEETS
Allowance for doubtful accounts | $	$ 2		$ 2
Materials and supplies, net of allowance | $	$ 148		$ 143
Shares, CHF par value (in Swiss francs per share) | SFr / shares		SFr 0.10		SFr 0.10
Shares, authorized	891,379,306		824,650,660
Shares, conditionally authorized	142,363,356		142,363,647
Shares, issued	685,676,456		639,676,165
Shares, outstanding	651,155,650		615,140,276