Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of the Company's beginning and ending amount of unrecognized tax benefits
Balance at the beginning of the period	$ 164	$ 156
Additions based on tax positions related to the current year	31	22
Additions for tax positions of prior years	10	69
Reductions for tax positions of prior years	(6)	(70)
Settlements	0	(10)
Business combinations	5	0
Lapse of statute of limitations	(11)	(3)
Foreign currency translation	(2)	0
Balance at the end of the period	$ 191	$ 164