Incentive Program (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum ownership of affiliates needed for awards	50.00%
Number of shares issuable under 2003 incentive program, maximum	220,000,000
Remaining shares available for award under 2003 incentive program	89,000,000
Options and stock appreciation rights grant, minimum percentage of market value, date of grant	100.00%
Share-based compensation arrangement by share-based payment award expiration period	10 years
Restricted Stock [Member]
Long-term incentive awards	8,916,000	9,583,000	9,681,000
Unrecognized compensation cost	$ 2,049
Unrecognized compensation cost, weighted-average period of recognition, years	4 years 6 months
Compensation cost charged against income	$ 856	$ 880	$ 855
Income tax benefit recognized in income	78	80	78
Fair value of shares/awards vested	826	851	808
Cash payments, vested restricted stock units	$ 64	$ 67	$ 64
Percent of the shares in each award vesting after three years	50.00%
Percent of the shares in each award vesting after seven years	50.00%
Percent of shares in each award vesting after five years	50.00%
Percent of shares in each award vesting in later of ten years or retirement	50.00%
Restricted Stock [Member] | Minimum [Member]
Vesting Period	3 years
Restricted Stock [Member] | Minimum [Member] | Executive Officer [Member]
Vesting Period	5 years
Restricted Stock [Member] | Maximum [Member]
Vesting Period	7 years
Restricted Stock [Member] | Maximum [Member] | Executive Officer [Member]
Vesting Period	10 years