Goodwill and other intangible assets (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Reconciliation of the changes in goodwill

Reconciliations of the changes in the carrying value of goodwill during 2017 and 2016 follows (in millions).

	December 31,
	2017		2016
Balance at beginning of year	$	79,486	$	62,708
Acquisitions of businesses		1,545		17,650
Other, including foreign currency translation		227		(872	)
Balance at end of year	$	81,258	$	79,486

Schedule of other intangible assets and related accumulated amortization

Our other intangible assets and related accumulated amortization are summarized as follows (in millions).

	December 31, 2017				December 31, 2016
	Gross carrying amount		Accumulated amortization		Gross carrying amount		Accumulated amortization
Insurance and other	$	40,225	$	7,707	$	39,976	$	6,495
Railroad, utilities and energy		988		324		898		293
	$	41,213	$	8,031	$	40,874	$	6,788
Trademarks and trade names	$	5,381	$	692	$	5,175	$	616
Patents and technology		4,341		2,493		4,341		2,328
Customer relationships		28,322		3,722		28,243		2,879
Other		3,169		1,124		3,115		965
	$	41,213	$	8,031	$	40,874	$	6,788