Debt and Equity Transactions (Unaudited) Early Extinguishment of debt (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 05, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Extinguishment of Debt [Line Items]
Write off of Deferred Debt Issuance Cost		$ 2
Extinguishment of Debt, Amount		266
Net gain on early extinguishment of debt		39		$ 0	$ 36	$ 0
Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Principal Amount		268
Extinguishment of Debt, Amount		268
Revolving Credit Facility [Member]
Extinguishment of Debt [Line Items]
Net gain on early extinguishment of debt			$ 3
5.450% Senior Notes due March 2043 [Member] | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Principal Amount		81
Write off of Deferred Debt Issuance Cost		1
Extinguishment of Debt, Amount		80
Net gain on early extinguishment of debt		16
3.55% Senior Notes due 2022 | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Principal Amount		85
Write off of Deferred Debt Issuance Cost		0
Extinguishment of Debt, Amount		85
Net gain on early extinguishment of debt		9
3.875% Senior Notes due March 2023 [Member] | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Principal Amount		52
Write off of Deferred Debt Issuance Cost		0
Extinguishment of Debt, Amount		52
Net gain on early extinguishment of debt		6
5.40% Senior Notes Due 2034 [Member] [Member] | Senior Notes [Member]
Extinguishment of Debt [Line Items]
Extinguishment of Debt, Principal Amount		50
Write off of Deferred Debt Issuance Cost		1
Extinguishment of Debt, Amount		49
Net gain on early extinguishment of debt		$ 8
Common Stock [Member]
Extinguishment of Debt [Line Items]
Proceeds from Issuance of Common Stock, Gross	$ 32						$ 2,000