Goodwill and other intangible assets - Changes During Period (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Changes in the carrying amount of goodwill [Abstract]
Balance at beginning of period	$ 47,453,000,000	$ 48,065,000,000	$ 47,647,000,000	$ 48,081,000,000
Changes during the period from:
Business combinations	9,000,000	9,000,000	17,000,000	18,000,000
Dispositions	0	0	(101,000,000)	0
Other	14,000,000	36,000,000	(87,000,000)	11,000,000
Balance at end of period	$ 47,476,000,000	$ 48,110,000,000	47,476,000,000	$ 48,110,000,000
Goodwill impairment			$ 0