Exhibit 12.1

	Nine Months Ended		Year Ended December 31,
	9/30/2017		2016		2015		2014			2013		2012
Earnings available for fixed charges:
Income (loss) before income taxes	$	1,935	$	3,892	$	1,568	$	(111	)	$	506	$	544
Fixed charges, excluding capitalized interest	$	638	$	598	$	547	$	283		$	197	$	133
Total earnings available for fixed charges	$	2,573	$	4,490	$	2,115	$	172		$	703	$	677
Fixed charges:
Interest and debt expense(1)	$	529	$	510	$	484	$	215		$	143	$	93
Assumed interest element included in rent expense	$	128	$	114	$	88	$	74		$	57	$	41
Total fixed charges	$	656	$	624	$	572	$	289		$	200	$	134
Ratio of earnings to fixed charges(2)		3.92		7.19		3.70		—			3.52		5.07

(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.