Income Taxes Reconciliation of Tax Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Gross tax contingencies - January 1	$ 710		$ 407	$ 294
Gross increases to tax positions in prior periods	254		351	78
Gross decreases to tax positions in prior periods	22		50	18
Gross increases to current period tax positions	242		20	54
Audit settlements paid	0		16	1
Lapse of statute of limitations	3		2	0
Gross tax contingencies - December 31	1,181	[1]	$ 710	$ 407
Tax contingencies, that if fully recognized, would decrease our effective tax rate	$ 882

[1] Deferred tax assets related to net operating losses and tax credits are presented net of tax contingencies.