Income Taxes - Unrecognized Tax Positions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in unrecognized tax positions
Balance, beginning of year	$ 8,000,000	$ 16,000,000	$ 269,000,000
Gross increases as a result of tax positions taken during prior periods	1,000,000	0	1,000,000
Gross decreases as a result of tax positions taken during prior periods	(4,000,000)	(10,000,000)	(256,000,000)
Gross increases as a result of tax positions taken during current period	2,000,000	2,000,000	2,000,000
Balance, end of year	7,000,000	8,000,000	16,000,000
Unrecognized tax positions disclosures
Unrecognized tax positions that would affect the effective tax rate	7,000,000	7,000,000	12,000,000
Interest and penalties recognized (reversed) as a component of income tax expense		$ (3,000,000)	(12,000,000)
Interest and penalties accrued	$ 0		$ 3,000,000