The changes in accumulated other comprehensive loss, presented net of tax, were as follows (in millions):

	Three months ended June 30, 2014								Three months ended June 30, 2013
	Defined benefit pension plans			Derivative instruments		Total			Defined benefit pension plans			Derivative instruments			Total
Balance, beginning of period	$	(263	)	$	—	$	(263	)	$	(533	)	$	(7	)	$	(540	)
Other comprehensive income (loss) before reclassifications	78			—		78			84			(1		)	83
Reclassifications to net income	(3		)	—		(3		)	12			11			23
Other comprehensive income, net	75			—		75			96			10			106
Balance, end of period	$	(188	)	$	—	$	(188	)	$	(437	)	$	3		$	(434	)

	Six months ended June 30, 2014									Six months ended June 30, 2013
	Defined benefit pension plans			Derivative instruments			Total			Defined benefit pension plans			Derivative instruments			Total
Balance, beginning of period	$	(264	)	$	2		$	(262	)	$	(511	)	$	(10	)	$	(521	)
Other comprehensive income (loss) before reclassifications	73			—			73			49			(5		)	44
Reclassifications to net income	3			(2		)	1			25			18			43
Other comprehensive income (loss), net	76			(2		)	74			74			13			87
Balance, end of period	$	(188	)	$	—		$	(188	)	$	(437	)	$	3		$	(434	)

Significant reclassifications from accumulated other comprehensive income to net income included the following (in millions):

		Three months ended June 30,						Six months ended June 30,
	Statement of operations classification	2014			2013			2014			2013
Defined benefit pension plans
Actuarial losses		$	6		$	14		$	12		$	28
Prior service costs		(1		)	(1		)	(1		)	(1		)
Settlements and curtailments		(5		)	—			(5		)	—
Total amortization, before income taxes	Net periodic benefit costs (a)	—			13			6			27
Income tax benefit	Income tax expense	(3		)	(1		)	(3		)	(2		)
Total amortization, net of income taxes		$	(3	)	$	12		$	3		$	25

(a) We recognize the amortization of accumulated other comprehensive income components related to defined benefit pension plans in net periodic benefit costs. In the three and six months ended June 30, 2014, the amortization components of our net periodic benefit costs were less than $1 million and $4 million, recorded in operating and maintenance costs, and less than $1 million and $2 million, recorded in general and administrative costs, respectively. In the three and six months ended June 30, 2013, the amortization components of our net periodic benefit costs were $10 million and $21 million, recorded in operating and maintenance costs, and $3 million and $6 million, recorded in general and administrative costs, respectively. See Note 12—Postemployment Benefit Plans.