Investments in debt and equity securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Schedule of available-for-sale securities

The cost basis and fair value of debt and equity securities were as follows:

	December 31, 2017							December 31, 2016
(Millions of dollars)	Cost Basis		Unrealized Pretax Net Gains (Losses)			Fair Value		Cost Basis		Unrealized Pretax Net Gains (Losses)			Fair Value
Government debt
U.S. treasury bonds	$	10	$	—		$	10	$	9	$	—		$	9
Other U.S. and non-U.S. government bonds	42		—			42		60		—			60
Corporate bonds
Corporate bonds	585		(1		)	584		489		3			492
Asset-backed securities	67		—			67		90		—			90
Mortgage-backed debt securities
U.S. governmental agency	265		(4		)	261		225		(2		)	223
Residential	8		—			8		10		—			10
Commercial	17		—			17		36		—			36
Equity securities
Large capitalization value	287		(3		)	284		280		32			312
Real estate investment trust (REIT)	104		6			110		77		2			79
Smaller company growth	40		16			56		41		15			56
Total	$	1,425	$	14		$	1,439	$	1,317	$	50		$	1,367

Investments in an unrealized loss position that are not other-than-temporarily impaired

Available-for-sale investments in an unrealized loss position that are not other-than-temporarily impaired:
	December 31, 2017
	Less than 12 months 1				12 months or more 1				Total
(Millions of dollars)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate bonds
Corporate bonds	$	312	$	2	$	38	$	—	$	350	$	2
Mortgage-backed debt securities
U.S. governmental agency	129		1		110		3		239		4
Equity securities
Large capitalization value	129		5		14		2		143		7
Smaller company growth	17		1		1		—		18		1
Total	$	587	$	9	$	163	$	5	$	750	$	14

	December 31, 2016
	Less than 12 months 1				12 months or more 1				Total
(Millions of dollars)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Corporate bonds
Corporate bonds	$	131	$	1	$	13	$	—	$	144	$	1
Mortgage-backed debt securities
U.S. governmental agency	167		2		11		—		178		2
Equity securities
Large capitalization value	68		6		11		2		79		8
Smaller company growth	10		1		3		1		13		2
Total	$	376	$	10	$	38	$	3	$	414	$	13

¹  Indicates length of time that individual securities have been in a continuous unrealized loss position.

Cost basis and fair value of the available-for-sale debt securities by contractual maturity

	December 31, 2017
(Millions of dollars)	Cost Basis		Fair Value
Due in one year or less	$	144	$	144
Due after one year through five years	418		417
Due after five years through ten years	121		120
Due after ten years	21		22
U.S. governmental agency mortgage-backed securities	265		261
Residential mortgage-backed securities	8		8
Commercial mortgage-backed securities	17		17
Total debt securities – available-for-sale	$	994	$	989

Schedule of proceeds and gross gain and losses from the sale of available-for-sale securities

Sales of Securities:
	Years Ended December 31,
(Millions of dollars)	2017		2016		2015
Proceeds from the sale of available-for-sale securities	$	930	$	694	$	351
Gross gains from the sale of available-for-sale securities	$	109	$	55	$	64
Gross losses from the sale of available-for-sale securities	$	5	$	4	$	2