Debt Debt (First Lien Notes) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
First Lien Notes 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 0	[1]	$ 320	[1]
Debt Instrument, Interest Rate, Effective Percentage	0.00%	[2]	8.20%	[2]
First Lien Notes 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt	0	[1]	875	[1]
Debt Instrument, Interest Rate, Effective Percentage	0.00%	[2]	8.20%	[2]
First Lien Notes 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt	0	[1]	1,600	[1]
Debt Instrument, Interest Rate, Effective Percentage	0.00%	[2]	7.70%	[2]
2022 First Lien Notes [Member]
Debt Instrument [Line Items]
Long-term Debt	745		744
Debt Instrument, Interest Rate, Effective Percentage	6.30%	[2]	6.20%	[2]
First Lien Notes 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt	840	[3]	960	[3]
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	10.00%
Debt Instrument, Interest Rate, Effective Percentage	8.00%	[2]	8.00%	[2]
2024 First Lien Notes [Member]
Debt Instrument [Line Items]
Long-term Debt	490		490
Debt Instrument, Interest Rate, Effective Percentage	6.00%	[2]	5.90%	[2]
Corporate Debt Securities [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 2,075		$ 4,989

[1] The 2019 First Lien Notes, 2020 First Lien Notes and 2021 First Lien Notes were repaid during the third quarter of 2014 with the proceeds from the issuance of our Senior Unsecured Notes, together with cash on hand, which are described in further detail below.

[2] Our weighted average interest rate calculation includes the amortization of deferred financing costs and debt discount.

[3] In December 2014, we used cash on hand to redeem 10% of the original aggregate principal amount of our 2023 First Lien Notes, plus accrued and unpaid interest. On February 3, 2015, we additionally repurchased approximately $150 million of our 2023 First Lien Notes with the proceeds from our 2024 Senior Unsecured Notes, which is described in further detail below.