CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Accounts receivable, allowance	$ 165	$ 178
Preferred stock-non-redeemable, par value (in dollars per share)	$ 25.00	$ 25.00
Preferred stock-non-redeemable, shares authorized	2,000	2,000
Preferred stock-non-redeemable, shares issued	7	7
Preferred stock-non-redeemable, shares outstanding	7	7
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized	1,600,000	1,600,000
Common stock, shares issued	549,654	546,545
Common stock, shares outstanding	549,654	546,545
Customer relationships
Finite-lived intangible assets, accumulated amortization	$ 6,902	$ 6,318
Other intangible assets
Finite-lived intangible assets, accumulated amortization	$ 2,256	$ 2,042