Goodwill and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015			2014
Balance at beginning of year	$	60,714		$	57,011
Acquisitions of businesses		2,563			4,006
Other, including foreign currency translation		(569	)		(303	)
Balance at end of year	$	62,708		$	60,714

Schedule of intangible assets

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

	December 31, 2015				December 31, 2014
	Gross carrying amount		Accumulated amortization		Gross carrying amount		Accumulated amortization
Insurance and other	$	14,610	$	5,462	$	13,667	$	4,464
Railroad, utilities and energy		888		239		2,254		1,551
	$	15,498	$	5,701	$	15,921	$	6,015
Trademarks and trade names	$	3,041	$	765	$	3,105	$	599
Patents and technology		4,252		2,050		5,425		3,133
Customer relationships		5,474		2,131		5,573		1,757
Other		2,731		755		1,818		526
	$	15,498	$	5,701	$	15,921	$	6,015