Background and Basis of Presentation (Share Repurchase Table) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Total number of shares repurchased (shares)	7.6	14.4	15.6	22.1
Aggregate cost of shares repurchased	$ 437	$ 1,049	$ 950	$ 1,600	$ 2,917
Average price per share of shares repurchased (usd per share)	$ 57.65	$ 72.85	$ 61.07	$ 72.47

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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