Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Estimated annual effective tax rate (as a percent)	25.00%	29.50%	25.50%
Prior year tax adjustment expense (benefit)	$ 42
Tax Year Prior Years
Income Tax Contingency [Line Items]
Income tax examination, proposed liability increase/(decrease)	1,000
Income tax adjustment	$ 125