Income Taxes (Current and Deferred Amounts of Provision) (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	[1]	Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Current:
Federal													$ (256)	$ (20)		$ (1)
State and municipal													(22)	(21)		(17)
Foreign													(196)	(317)		(287)
Deferred:
Federal													(34)	(1,617)		310
State and municipal													4	(109)		48
Foreign													67	(70)		(50)
(Provision) benefit for income taxes	$ (54)	$ (133)	$ (126)	$ (124)	$ (1,978)		$ (89)		$ (153)		$ 66		$ (437)	$ (2,154)	[1]	$ 3

[1] In December 2017, the U.S. enacted the 2017 Tax Act which resulted in significant changes to our provision for income taxes during the fourth quarter of 2017. Refer to Note 4 (Income Taxes) to the Consolidated Financial Statements for additional information.