Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 6,309	$ 6,301
Less: amount due within one year	1,404	405
Total long-term debt	$ 4,905	5,896
1.63% Convertible Notes, due 2019
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	1.63%
Long-term debt	$ 403	403
6.150% Notes, due 2020
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	6.15%
Long-term debt	$ 1,000	1,000
5.40% Notes due 2021
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	5.40%
Long-term debt	$ 1,250	1,250
5.87% Notes, due 2022
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	5.87%
Long-term debt	$ 627	627
5.125% Notes, due 2024
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	5.125%
Long-term debt	$ 1,250	1,250
5.90% Notes, due 2027
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	5.90%
Long-term debt	$ 625	625
6.75% Bonds, due 2028
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	6.75%
Long-term debt	$ 300	300
5.95% Notes, due 2037
Debt Instrument [Line Items]
Long-term debt, interest rate (percentage)	5.95%
Long-term debt	$ 625	625
Iowa Finance Authority Loan, due 2042
Debt Instrument [Line Items]
Long-term debt	250	250
Other
Debt Instrument [Line Items]
Other	$ (21)	$ (29)

Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt classified as other.

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