Schedule II - Condensed Financial Information, Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
Total operating expenses	$ 2,802	$ 2,655
Income before Income Taxes	1,218	890
Income tax expense (benefit)	301	297
Shareholders' Net Income	915	598
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities	(279)	7
Net unrealized appreciation (depreciation) on derivatives	(5)	(3)
Net translation of foreign currencies	45	112
Postretirement benefits liability adjustment	13	14
Shareholders' other comprehensive income (loss)	(226)	130
Shareholders' comprehensive income (loss)	$ 689	$ 728