Basis of Presentation and Significant Accounting Policies and Practices - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Basic EPS:
Net income	$ 997	$ 711
Income allocated to RSUs	(10)	(9)
Income allocated to common stock for basic EPS calculation	$ 987	$ 702
Weighted average number of shares outstanding, basic (in shares)	998	1,007
Basic earnings per common share	$ 0.99	$ 0.70
Adjustment for dilutive shares:
Stock compensation plans	21	15
Diluted EPS:
Net income	$ 997	$ 711
Income allocated to RSUs	(10)	(9)
Income allocated to common stock for diluted EPS	$ 987	$ 702
Weighted average number of shares outstanding, diluted (in shares)	1,019	1,022
Diluted earnings per common share	$ 0.97	$ 0.69

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Amount of undistributed earnings (loss) allocated to participating securities for the diluted earnings (loss) per share or per unit calculation under the two-class method.

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