Debt and Lines of Credit (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Long-term Debt Instruments

Long-term debt outstanding is as follows:

	December 31,
	2017			2016
Notes due 2017 at 0.875%	$	—		$	250
Notes due 2017 at 6.60% (assumed with National acquisition)		—			375
Notes due 2018 at 1.00%		500			500
Notes due 2019 at 1.65%		750			750
Notes due 2020 at 1.75%		500			500
Notes due 2021 at 2.75%		550			250
Notes due 2022 at 1.85%		500			500
Notes due 2023 at 2.25%		500			500
Notes due 2024 at 2.625%		300			—
Notes due 2027 at 2.90%		500			—
Total debt		4,100			3,625
Net unamortized discounts, premiums and debt issuance costs		(23	)		(16	)
Total debt, including net unamortized discounts, premiums and debt issuance costs		4,077			3,609
Current portion of long-term debt		(500	)		(631	)
Long-term debt	$	3,577		$	2,978