Comprehensive Income and Shareholders' Equity (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		$ 2,531	$ 2,858	$ 1,383
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		25,413	21,540	21,350
Cumulative effect of accounting changes		30
Other comprehensive income (loss) before reclassifications		(431)
Amounts reclassified from accumulated other comprehensive items		24
Total other comprehensive items		(407)	633	(639)
Balance	$ 25,413	$ 27,586	25,413	21,540
Class of Stock Disclosures [Abstract]
Common Stock, Capital Shares Reserved for Future Issuance (in shares)		30
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		$ (1,755)
Cumulative effect of accounting changes		(54)
Other comprehensive income (loss) before reclassifications		(434)
Total other comprehensive items		(434)
Balance	(1,755)	(2,243)	(1,755)
Unrealized Gains on Available-for-Sale Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(1)
Cumulative effect of accounting changes		1
Total other comprehensive items		0
Balance	(1)	0	(1)
Unrealized Losses on Hedging Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(50)
Cumulative effect of accounting changes		(11)
Amounts reclassified from accumulated other comprehensive items		9
Total other comprehensive items		9
Balance	(50)	(52)	(50)
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(197)
Cumulative effect of accounting changes		(24)
Other comprehensive income (loss) before reclassifications		3
Amounts reclassified from accumulated other comprehensive items		15
Total other comprehensive items		18
Balance	(197)	(203)	(197)
Accumulated Other Comprehensive Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance		(2,003)	(2,636)	(1,997)
Cumulative effect of accounting changes		(88)
Total other comprehensive items		(407)	633	(639)
Balance	(2,003)	$ (2,498)	$ (2,003)	$ (2,636)
Income Taxes on Net Investment Hedge [Member] | Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 101