CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Accounts receivable, allowance	$ 180	$ 178
Preferred stock-non-redeemable, par value (per share)	$ 25.00	$ 25.00
Preferred stock-non-redeemable, authorized shares	2,000	2,000
Preferred stock-non-redeemable, issued shares	7	7
Preferred stock-non-redeemable, outstanding shares	7	7
Common stock, par value (per share)	$ 1.00	$ 1.00
Common stock, authorized shares	1,600,000	1,600,000
Common stock, issued shares	548,845	546,545
Common stock, outstanding shares	548,845	546,545
Customer relationships
Finite-lived intangible assets, accumulated amortization	$ 6,519	$ 6,318
Other intangible assets
Finite-lived intangible assets, accumulated amortization	$ 2,105	$ 2,042