Schedule II - Condensed Financial Information, Statements of Income (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 30, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Debt extinguishment costs	$ 100		$ 321							$ 321	$ 0	$ 100
Total operating expenses										10,033	9,584	8,982
Income before Income Taxes		$ 758	824	$ 1,134	$ 890	$ 605	$ 742	$ 813	$ 819	3,606	2,979	3,327
Income tax expense (benefit)										1,374	1,136	1,250
Shareholders' Net Income		$ 266	$ 560	$ 813	$ 598	$ 382	$ 456	$ 510	$ 519	2,237	1,867	2,094
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities										(34)	(56)	(202)
Net unrealized appreciation (depreciation) on derivatives										(3)	(4)	15
Net translation of foreign currencies										304	(95)	(212)
Postretirement benefits liability adjustment										33	23	85
Shareholders' other comprehensive income (loss)										300	(132)	(314)
Shareholders' comprehensive income (loss)										2,537	1,735	1,780
Parent Company [Member]
Operating expenses:
Interest										237	244	246
Intercompany interest										18	3	2
Debt extinguishment costs										321	0	100
Other										204	281	147
Total operating expenses										780	528	495
Income before Income Taxes										(780)	(528)	(495)
Income tax expense (benefit)										(194)	(146)	(135)
(Loss) of parent company										(586)	(382)	(360)
Equity in income from subsidiaries										2,823	2,249	2,454
Shareholders' Net Income										2,237	1,867	2,094
Shareholders' other comprehensive income (loss), net of tax:
Net unrealized appreciation (depreciation) on securities										(34)	(56)	(202)
Net unrealized appreciation (depreciation) on derivatives										(3)	(4)	15
Net translation of foreign currencies										304	(95)	(212)
Postretirement benefits liability adjustment										33	23	85
Shareholders' other comprehensive income (loss)										300	(132)	(314)
Shareholders' comprehensive income (loss)										$ 2,537	$ 1,735	$ 1,780