Exhibit 12.1

Ratio of Earnings to Fixed Charges

(in millions)

	Three Months Ended 3/31/2018		Year Ended December 31,
			2017		2016		2015		2014			2013
Earnings available for fixed charges:
Income (loss) before income taxes	$	1,916	$	3,806	$	3,892	$	1,568	$	(111	)	$	506
Fixed charges, excluding capitalized interest	$	405	$	1,044	$	598	$	547	$	283		$	197
Total earnings available for fixed charges	$	2,321	$	4,850	$	4,490	$	2,115	$	172		$	703
Fixed charges:
Interest and debt expense (1)	$	338	$	875	$	510	$	484	$	215		$	143
Assumed interest element included in rent expense	$	75	$	195	$	114	$	88	$	74		$	57
Total fixed charges	$	413	$	1,070	$	624	$	572	$	289		$	200
Ratio of earnings to fixed charges (2)		5.62		4.53		7.19		3.70		—			3.52

(1) Includes amortization of debt-related expenses plus interest capitalized during the period.

(2) In 2014, our earnings were insufficient to cover fixed charges by $117 million.