Accounting Policies - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of cash flows from Operating Activities	$ (185)	$ (67)
Reclassification of cash flows to Financing Activities	426	172
Restricted cash balances	$ 66	15	$ 57
Accounting Standards Update 2016-15 | New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of cash flows from Operating Activities		(53)
Reclassification of cash flows to Financing Activities		$ 53