Segment Information (Financial Data By Reportable Segment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Reportable segments operating revenues	$ 103,141	$ 91,341	$ 89,061
Operating gain (loss)	5,999	5,426	4,175
Depreciation and amortization of property and equipment	675	652	601
Commercial and Specialty Business Segment [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	37,421	35,782	40,363
Operating gain (loss)	4,046	3,600	2,847
Depreciation and amortization of property and equipment	0	0	0
Government Business Segment [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	62,632	55,348	48,587
Operating gain (loss)	2,054	1,928	1,442
Depreciation and amortization of property and equipment	0	0	0
Other [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	7,695	1,519	127
Operating gain (loss)	(101)	(102)	(114)
Depreciation and amortization of property and equipment	675	652	601
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	(4,607)	(1,308)	(16)
Affiliated [Member] | Other [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	4,607	1,308	16
Other [Member] | Unaffiliated [Member]
Segment Reporting Information [Line Items]
Reportable segments operating revenues	$ 3,088	$ 211	$ 111