Quarterly Financial Data (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015
Restructuring Cost and Reserve [Line Items]
Impairment and restructuring, after tax	$ 13		$ 8	$ 8
Impairment and restructuring per share, after tax	$ 0.03		$ 0.01	$ 0.01
Employee benefit curtailment, after tax	$ 24
Employee benefit curtailment, per share	$ 0.04
Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes		$ (9)	$ 101		$ 421	$ 23	$ 71
Gain (loss) on sale of assets, after tax, per share		$ (0.02)	$ 0.17		$ 0.70	$ 0.04	$ 0.11
Impairment, settlement, and restructuring, after tax		$ 48
Impairment, settlement, and restructuring per share, after tax		$ 0.08
Equity Sold, Percentage							50.00%
Asset abandonments and impairments, after tax					$ 50	$ 35	$ 28
Impairment Effect on Earnings Per Share, after Tax					$ 0.08	$ 0.06	$ 0.04
Out of period tax discrete expense (income) items	$ 21		$ 6		$ (73)		$ 13
Out of period tax discrete expense (income) items, per share	$ 0.03		$ 0.01		$ (0.12)		$ 0.02
Restructuring and exit costs, after tax					$ 33	$ 26
Restructuring and exit costs, after tax, per share					$ 0.06	$ 0.04
Extinguishment of Debt, Gain (Loss), Net of Tax						$ 118
Extinguishment of Debt, Gain (Loss), Per Share, Net of Tax						$ 0.19
Other Charges, After Tax					$ 58
Other Charges, After Tax, Per Share					$ 0.10