Stockholders' Equity - Stock Repurchase Program (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018	Jan. 28, 2016
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock, amount		$ 2,067
2016 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Authorized amount			$ 12,000
Repurchases of common stock (in shares)	6	26
Repurchases of common stock, amount	$ 449	$ 1,900
Remaining authorized repurchase amount	$ 6,100	$ 6,100

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration