Debt (Schedule of Debt Extinguishment) (Details) - Senior Notes [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Extinguishment of Debt [Line Items]
Notes Purchased	$ 933	$ 793	$ 933	$ 793
9.95% Senior Notes Due 2038 [Member]
Extinguishment of Debt [Line Items]
Notes Purchased			441	0
10.20% Senior Notes Due 2039 [Member]
Extinguishment of Debt [Line Items]
Notes Purchased			492	0
9.70% Senior Notes Due 2018 [Member]
Extinguishment of Debt [Line Items]
Notes Purchased			$ 0	$ 793