9. Intangible Assets

The carrying amounts of identifiable intangible assets are summarized as follows:

(in millions)	Indefinite-lived		Finite-lived			Total
December 31, 2016	$	17,178	$	185		$	17,363
Amortization expense		—		(50	)		(50	)
Acquisition⁽¹⁾		—		110			110
June 30, 2017	$	17,178	$	245		$	17,423

⁽¹⁾ In connection with the First Reserve Transaction, the Company acquired $110 million of finite-lived assets with a weighted-average estimated life of approximately nine years.