Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the Company's beginning and ending amount of unrecognized tax benefits
Balance at the beginning of the period	$ 238	$ 211
Additions based on tax positions related to the current year	36	31
Additions for tax positions of prior years	20	53
Reductions for tax positions of prior years	(12)	(18)
Settlements	0	(32)
Business combinations	2	0
Lapse of statute of limitations	(5)	(5)
Foreign currency translation	(1)	(2)
Balance at the end of the period	$ 278	$ 238