Goodwill and other intangible assets - Changes During Period (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Goodwill [Roll Forward]
Balance at beginning of period	$ 47,476,000,000	$ 48,110,000,000	$ 47,647,000,000	$ 48,081,000,000
Changes during the period from:
Business combinations	8,000,000	6,000,000	25,000,000	24,000,000
Dispositions	0	(1,000,000)	(101,000,000)	(1,000,000)
Other	(79,000,000)	(145,000,000)	(166,000,000)	(134,000,000)
Balance at end of period	47,405,000,000	47,970,000,000	47,405,000,000	47,970,000,000
Goodwill impairment			0
Corporate
Goodwill [Roll Forward]
Balance at beginning of period			101,000,000
Changes during the period from:
Balance at end of period	$ 0		$ 0
Goodwill impairment		$ 68,000,000		$ 68,000,000