Goodwill and Intangible Assets - Actual and Estimated Future Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Actual for the year ended December 31,
Actual amortization expense	$ 430	$ 532	$ 671
Estimated future amounts for the year ended December 31,
2016	368
2017	269
2018	178
2019	100
2020	49
Thereafter	73
Net Carrying Amount	$ 1,037