Accounting Changes - Intra-Entity Transfers (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2017 item	Mar. 31, 2018 USD ($) item $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares		Jan. 01, 2017 USD ($)
Accounting Changes
Investments and sundry assets		$ 2,942		$ 2,783	[1]
Prepaid expenses and other current assets		2,573		1,860	[1],[2]
Deferred tax assets		5,111		4,862
Retained earnings		156,371		153,126
Continuing operations provision for (benefit from) income taxes		(540)	$ (329)
Income from continuing operations		1,675	1,753
Net income		$ 1,679	$ 1,750
Earnings per share, basic (in dollars per share) | $ / shares		$ 1.82	$ 1.86
Earnings per share, diluted (in dollars per share) | $ / shares		$ 1.81	$ 1.85
Accounting Standards Update 2016-16, Intra-Entity Transfers of Assets Other Than Inventory
Accounting Changes
Number of transactions within scope of new guidance | item		0
Accounting Standards Update 2016-16, Intra-Entity Transfers of Assets Other Than Inventory | Early adoption
Accounting Changes
Investments and sundry assets						$ (95)
Prepaid expenses and other current assets						(47)
Deferred tax assets						244
Retained earnings						$ 102
Number of transactions within scope of new guidance | item	1
Continuing operations provision for (benefit from) income taxes			$ (582)	(582)
Income from continuing operations				582
Net income				$ 582
Earnings per share, basic (in dollars per share) | $ / shares			$ 0.62	$ 0.62
Earnings per share, diluted (in dollars per share) | $ / shares			$ 0.61	$ 0.62

[1] Recast to conform to current period presentation.

[2] Recast to reflect adoption of the FASB guidance on restricted cash.