Income Taxes Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Contingency [Line Items]
Gross unrecognized tax benefits, beginning of period	$ 92	$ 89	$ 81
Current year tax positions	0	0	8
Prior year tax positions, gross increases	55	4	5
Acquired Reserves	89	0	0
Prior year tax positions, gross decreases	(2)	0	0
Settlements	(1)	0	0
Statute of limitations lapses	(9)	(1)	(5)
Gross unrecognized tax benefits, end of period	$ 224	$ 92	$ 89