Income Taxes (Current and deferred components of the Company's income tax (expense) benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current tax expense	$ (243)	$ (142)	$ (220)
Deferred tax benefit (expense)	(168)	(136)	150
Income tax expense	$ (411)	$ (278)	$ (70)