Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Consolidated Quarterly Results [Abstract]
Total revenues	$ 9,880	$ 9,389	$ 29,724	$ 28,348
Income before income taxes	742	878	2,374	2,668
Shareholders' net income	$ 456	$ 547	$ 1,485	$ 1,668
Shareholders' Net Income Per Share:
EPS, basic	$ 1.78	$ 2.14	$ 5.82	$ 6.51
EPS, diluted	1.76	2.10	5.72	6.40
Stock And Dividend Data [Abstract]
Dividends Declared Per Share	$ 0	$ 0	$ 0.04	$ 0.04
Quarterly Financial Data Text Details [Abstract]
Debt extinguishment costs				$ 65
Merger-related transaction costs	$ 46	$ 29	$ 108	$ 29