Goodwill and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill and Intangible Assets Disclosure [Abstract]

Reconciliation of the change in goodwill

A reconciliation of the change in the carrying value of goodwill is as follows (in millions).

	December 31,
	2016			2015
Balance at beginning of year	$	62,708		$	60,714
Acquisitions of businesses		17,650			2,563
Other, including foreign currency translation		(872	)		(569	)
Balance at end of year	$	79,486		$	62,708

Schedule of intangible assets

Other intangible assets are summarized as follows (in millions).

	December 31, 2016				December 31, 2015
	Gross carrying amount		Accumulated amortization		Gross carrying amount		Accumulated amortization
Insurance and other	$	39,976	$	6,495	$	14,610	$	5,462
Railroad, utilities and energy		898		293		888		239
	$	40,874	$	6,788	$	15,498	$	5,701
Trademarks and trade names	$	5,175	$	616	$	3,041	$	765
Patents and technology		4,341		2,328		4,252		2,050
Customer relationships		28,243		2,879		5,474		2,131
Other		3,115		965		2,731		755
	$	40,874	$	6,788	$	15,498	$	5,701