Goodwill and Intangible Assets (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Goodwill and Intangible Assets [Line Items]
Goodwill, beginning of the period				$ 28,142
Goodwill acquired during period				9,035
Goodwill, Translation Adjustments				(40)
Goodwill, Other Changes	[1]			(2)
Goodwill, end of the period		$ 37,135		37,135
Indefinite-Lived Intangible Assets (Excluding Goodwill)		6,398		6,398		$ 6,398
Intangible Assets, Gross (Excluding Goodwill)		18,021		18,021		13,799
Finite-Lived Intangible Assets, Accumulated Amortization		(4,517)		(4,517)		(4,025)
Intangible Assets, Net (Excluding Goodwill)		13,504		$ 13,504		9,774
Finite-Lived Intangible Asset, Useful Life				15 years 7 months
Amortization		160	$ 126	$ 419	$ 391
Pharmacy Services Segment
Goodwill and Intangible Assets [Line Items]
Goodwill, beginning of the period				21,234
Goodwill acquired during period				444
Goodwill, Translation Adjustments				0
Goodwill, Other Changes	[1]			(1)
Goodwill, end of the period		21,677		21,677
Retail/LTC Segment [Member]
Goodwill and Intangible Assets [Line Items]
Goodwill, beginning of the period				6,908
Goodwill acquired during period				8,591
Goodwill, Translation Adjustments				(40)
Goodwill, Other Changes	[1]			(1)
Goodwill, end of the period		15,458		15,458
Customer Contracts Relationships and Covenants Not to Compete [Member]
Goodwill and Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)		10,536		10,536		6,521
Finite-Lived Intangible Assets, Accumulated Amortization		(3,921)		(3,921)		(3,549)
Intangible Assets, Net (Excluding Goodwill)		6,615		$ 6,615		2,972
Finite-Lived Intangible Asset, Useful Life				15 years 7 months
Favorable Leases and Other [Member]
Goodwill and Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)		1,087		$ 1,087		880
Finite-Lived Intangible Assets, Accumulated Amortization		(596)		(596)		(476)
Intangible Assets, Net (Excluding Goodwill)		$ 491		$ 491		$ 404

[1] "Other" represents immaterial purchase accounting adjustments for acquisitions.