Shareholders' Equity - Accounting for Share-based Compensation (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Equity [Abstract]
Share-based payment award tax benefit	$ (236)

Effective Income Tax Rate Reconciliation Share-based Compensation Excess Tax Benefit Amount

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration