CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) $ in Millions	Mar. 31, 2021 USD ($) shares	Mar. 31, 2021 SFr / shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2020 SFr / shares
CONDENSED CONSOLIDATED BALANCE SHEETS
Allowance for doubtful accounts | $	$ 2		$ 2
Materials and supplies, net of allowance | $	$ 144		$ 143
Shares, CHF par value (in Swiss francs per share) | SFr / shares		SFr 0.10		SFr 0.10
Shares, authorized	824,650,668		824,650,660
Shares, conditionally authorized	142,363,647		142,363,647
Shares, issued	639,676,165		639,676,165
Shares, outstanding	617,288,705		615,140,276