Derivatives and Hedging Activities and Fair Value Measurement - Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Total Assets	$ 49	$ 48
Total Liabilities	4	6
Long-term debt	632	1,221
Trade and Other Payables [Member]
Derivative [Line Items]
Stock-based compensation - liability awards	4	5
Other Liabilities and Deferred Credits [Member]
Derivative [Line Items]
Stock-based compensation - liability awards	13	11
Long Term Debt Due within One Year [Member]
Derivative [Line Items]
Long-term debt	312	13
Currency Derivatives [Member] | Prepaid Expenses [Member]
Derivative [Line Items]
Total Assets	34	31
Currency Derivatives [Member] | Other Assets [Member]
Derivative [Line Items]
Total Assets	14	16
Currency Derivatives [Member] | Trade and Other Payables [Member]
Derivative [Line Items]
Total Liabilities	1	1
Natural Gas Swap Contracts [Member] | Prepaid Expenses [Member]
Derivative [Line Items]
Total Assets	1
Natural Gas Swap Contracts [Member] | Other Assets [Member]
Derivative [Line Items]
Total Assets		1
Natural Gas Swap Contracts [Member] | Trade and Other Payables [Member]
Derivative [Line Items]
Total Liabilities	1	2
Natural Gas Swap Contracts [Member] | Other Liabilities and Deferred Credits [Member]
Derivative [Line Items]
Total Liabilities	2	3
Equity Swap Contracts [Member] | Other Assets [Member]
Derivative [Line Items]
Equity swap contracts	5	2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Trade and Other Payables [Member]
Derivative [Line Items]
Stock-based compensation - liability awards	4	5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Liabilities and Deferred Credits [Member]
Derivative [Line Items]
Stock-based compensation - liability awards	13	11
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Swap Contracts [Member] | Other Assets [Member]
Derivative [Line Items]
Equity swap contracts	5	2
Significant Observable Inputs (Level 2) [Member]
Derivative [Line Items]
Total Assets	49	48
Total Liabilities	4	6
Long-term debt	632	1,221
Significant Observable Inputs (Level 2) [Member] | Long Term Debt Due within One Year [Member]
Derivative [Line Items]
Long-term debt	312	13
Significant Observable Inputs (Level 2) [Member] | Currency Derivatives [Member] | Prepaid Expenses [Member]
Derivative [Line Items]
Total Assets	34	31
Significant Observable Inputs (Level 2) [Member] | Currency Derivatives [Member] | Other Assets [Member]
Derivative [Line Items]
Total Assets	14	16
Significant Observable Inputs (Level 2) [Member] | Currency Derivatives [Member] | Trade and Other Payables [Member]
Derivative [Line Items]
Total Liabilities	1	1
Significant Observable Inputs (Level 2) [Member] | Natural Gas Swap Contracts [Member] | Prepaid Expenses [Member]
Derivative [Line Items]
Total Assets	1
Significant Observable Inputs (Level 2) [Member] | Natural Gas Swap Contracts [Member] | Other Assets [Member]
Derivative [Line Items]
Total Assets		1
Significant Observable Inputs (Level 2) [Member] | Natural Gas Swap Contracts [Member] | Trade and Other Payables [Member]
Derivative [Line Items]
Total Liabilities	1	2
Significant Observable Inputs (Level 2) [Member] | Natural Gas Swap Contracts [Member] | Other Liabilities and Deferred Credits [Member]
Derivative [Line Items]
Total Liabilities	$ 2	$ 3