Taxes on Income - Current and Deferred (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure
Federal													$ 21	$ 258	$ (52)
State													0	32	(7)
Current Income Tax Expense (Benefit)													21	290	(59)
Federal													17	(130)	119
State													14	22	38
Deferred income taxes													31	(108)	157
Total income tax expense	$ 17	$ 23	$ 0	$ 12	$ 47	$ 8	$ 23	$ 104	$ 12	$ 127	$ 35	$ 135	$ 52	$ 182	$ 98