Goodwill and Other Intangible Assets (Tables)

The gross carrying amounts of goodwill and accumulated impairment associated with our contract drilling services reporting unit were as follows (in millions):

	Year ended December 31, 2013							Year ended December 31, 2012
	Gross carrying amount		Accumulated impairment			Net carrying amount		Gross carrying amount			Accumulated impairment			Net carrying amount
Balance, beginning of period	$	10,799	$	(7,812	)	$	2,987	$	10,911		$	(7,694	)	$	3,217
Impairment associated with continuing operations	—		—			—		—			(118		)	(118		)
Reclassified balance associated with discontinued operations (a)	—		—			—		(112		)	—			(112		)
Balance, end of period	$	10,799	$	(7,812	)	$	2,987	$	10,799		$	(7,812	)	$	2,987

(a) As a result of our decision to discontinue operations associated with the standard jackups and swamp barge asset groups, components of our contract drilling services operating segment, we allocated $112 million of goodwill attributable to such operations, which was subsequently impaired. See Note 7—Discontinued Operations.

The gross carrying amounts of our drilling contract intangibles and drilling management customer relationships, both of which we consider to be definite-lived intangible assets and intangible liabilities, and accumulated amortization and impairment were as follows (in millions):

	Year ended December 31, 2013								Year ended December 31, 2012
	Gross carrying amount		Accumulated amortization and impairment			Net carrying amount			Gross carrying amount			Accumulated amortization and impairment			Net carrying amount
Drilling contract intangible assets
Balance, beginning of period	$	9	(9		)	—			$	191		$	(191	)	$	—
Amortization	—		—			—			—			—			—
Reclassified balance associated with discontinued operations (a)	—		—			—			(182		)	182			—
Balance, end of period	9		(9		)	—			9			(9		)	—

Customer relationships
Balance, beginning of period	60		(60		)	—			148			(94		)	54
Amortization	—		—			—			—			(1		)	(1		)
Impairment associated with continuing operations	—		—			—			—			(22		)	(22		)
Reclassified balance associated with discontinued operations (b)	—		—			—			(88		)	57			(31		)
Balance, end of period	60		(60		)	—			60			(60		)	—

Total definite-lived intangible assets
Balance, beginning of period	69		(69		)	—			339			(285		)	54
Amortization	—		—			—			—			(1		)	(1		)
Impairment associated with continuing operations	—		—			—			—			(22		)	(22		)
Reclassified balance associated with discontinued operations (b)	—		—			—			(270		)	239			(31		)
Balance, end of period	$	69	(69		)	—			$	69		$	(69	)	$	—

Drilling contract intangible liabilities
Balance, beginning of period	$	1,410	$	(1,351	)	$	59		$	1,494		$	(1,393	)	$	101
Amortization	—		(15		)	(15		)	—			(42		)	(42		)
Reclassified balance associated with discontinued operations (a)	—		—			—			(84		)	84			—
Balance, end of period	$	1,410	$	(1,366	)	$	44		$	1,410		$	(1,351	)	$	59

(a) As a result of our decision to discontinue operations associated with the standard jackup and swamp barge asset groups, we reclassified the balances attributable to such operations. See Note 7—Discontinued Operations.

(b) As a result of our decision to discontinue the U.S. operations of our drilling management services operating segment, we reclassified the balances attributable to such operations. See Note 7—Discontinued Operations.

At December 31, 2013, the estimated future amortization of our drilling contract intangible liabilities was as follows (in millions):

	Drilling contract intangible liabilities
Years ending December 31,
2014	$	15
2015	15
2016	14
Total intangible liabilities	$	44