Fair Value Measurements - Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets:
Gross derivative assets	$ 765.3	$ 378.5
Liabilities:
Gross derivative liabilities	783.1	349.5
Fair value measured on recurring basis
Assets:
Total assets at fair value	779.4	389.9
Liabilities:
Total liabilities at fair value	783.1	349.5
Fair value measured on recurring basis | Level 1 Inputs
Assets:
Total assets at fair value	431.3	233.5
Liabilities:
Total liabilities at fair value	326.1	223.0
Fair value measured on recurring basis | Level 2 Inputs
Assets:
Total assets at fair value	346.0	146.8
Liabilities:
Total liabilities at fair value	454.4	120.2
Fair value measured on recurring basis | Level 3 Inputs
Assets:
Total assets at fair value	2.1	9.5
Liabilities:
Total liabilities at fair value	2.6	6.3
Commodity contracts | Fair value measured on recurring basis
Assets:
Gross derivative assets	758.4	371.0
Liabilities:
Gross derivative liabilities	777.8	326.0
Commodity contracts | Fair value measured on recurring basis | Level 1 Inputs
Assets:
Gross derivative assets	431.3	233.5
Liabilities:
Gross derivative liabilities	326.1	223.0
Commodity contracts | Fair value measured on recurring basis | Level 2 Inputs
Assets:
Gross derivative assets	325.0	127.9
Liabilities:
Gross derivative liabilities	449.1	96.8
Commodity contracts | Fair value measured on recurring basis | Level 3 Inputs
Assets:
Gross derivative assets	2.1	9.5
Liabilities:
Gross derivative liabilities	2.6	6.3
Foreign currency contracts | Fair value measured on recurring basis
Assets:
Gross derivative assets	4.5	7.5
Liabilities:
Gross derivative liabilities	4.0	19.8
Foreign currency contracts | Fair value measured on recurring basis | Level 1 Inputs
Assets:
Gross derivative assets	0.0	0.0
Liabilities:
Gross derivative liabilities	0.0	0.0
Foreign currency contracts | Fair value measured on recurring basis | Level 2 Inputs
Assets:
Gross derivative assets	4.5	7.5
Liabilities:
Gross derivative liabilities	4.0	19.8
Foreign currency contracts | Fair value measured on recurring basis | Level 3 Inputs
Assets:
Gross derivative assets	0.0	0.0
Liabilities:
Gross derivative liabilities	0.0	0.0
Interest rate contracts | Fair value measured on recurring basis
Assets:
Gross derivative assets	2.4
Liabilities:
Gross derivative liabilities	1.3	3.7
Interest rate contracts | Fair value measured on recurring basis | Level 1 Inputs
Assets:
Gross derivative assets	0.0
Liabilities:
Gross derivative liabilities	0.0	0.0
Interest rate contracts | Fair value measured on recurring basis | Level 2 Inputs
Assets:
Gross derivative assets	2.4
Liabilities:
Gross derivative liabilities	1.3	3.7
Interest rate contracts | Fair value measured on recurring basis | Level 3 Inputs
Assets:
Gross derivative assets	0.0
Liabilities:
Gross derivative liabilities	0.0	0.0
Cash surrender value of life insurance | Fair value measured on recurring basis
Assets:
Cash surrender value of life insurance	14.1	11.4
Cash surrender value of life insurance | Fair value measured on recurring basis | Level 1 Inputs
Assets:
Cash surrender value of life insurance	0.0	0.0
Cash surrender value of life insurance | Fair value measured on recurring basis | Level 2 Inputs
Assets:
Cash surrender value of life insurance	14.1	11.4
Cash surrender value of life insurance | Fair value measured on recurring basis | Level 3 Inputs
Assets:
Cash surrender value of life insurance	$ 0.0	$ 0.0