Schedule II - Condensed Financial Information, Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses:
Total operating expenses	$ 2,893	$ 2,412	$ 5,695	$ 5,067
Income before Income Taxes	1,102	1,134	2,320	2,024
Income tax expense (benefit)	294	324	595	621
Shareholders' net income	806	813	1,721	1,411
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities	(141)	67	(420)	74
Net unrealized appreciation (depreciation), derivatives	(8)	0	(13)	(3)
Net translation of foreign currencies	(152)	27	(107)	139
Postretirement benefits liability adjustment	5	12	18	26
Shareholders' other comprehensive income (loss)	(296)	106	(522)	236
Shareholders' comprehensive income (loss)	$ 510	$ 919	$ 1,199	$ 1,647