Goodwill and Other Intangible Assets - Changes During Period (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in the carrying amount of goodwill [Abstract]
Balance at beginning of period	$ 47,647,000,000	$ 48,081,000,000	$ 48,175,000,000
Changes during the period:
Business combinations	28,000,000	43,000,000	64,000,000
Dispositions	(160,000,000)	(80,000,000)	(5,000,000)
Other	(190,000,000)	(397,000,000)	(153,000,000)
Balance at end of period	47,325,000,000	47,647,000,000	48,081,000,000
Corporate
Changes in the carrying amount of goodwill [Abstract]
Balance at beginning of period	101,000,000	377,000,000
Changes during the period:
Balance at end of period	$ 0	101,000,000	377,000,000
Goodwill impairment loss		$ 276,000,000	$ 0