Capital Stock (Schedule of Shares Repurchased) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Total number of shares repurchased (in shares)	27,878,324	41,604,141	16,221,001
Aggregate cost of shares repurchased	$ 1,673	$ 2,917	$ 1,030
Average price per share of shares repurchased (USD per share)	$ 60.00	$ 70.10	$ 63.48

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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