Statutory Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statutory Accounting Practices [Line Items]
Dividends available to be paid	$ 5,800
Approximate increase in statutory capital and surplus resulting from discount of certain A&E liabilities	169	$ 155
Minimum statutory capital and surplus required to satisfy regulatory requirements	23,900	22,200
Statutory Accounting Practices, Permitted Practice, Amount	156	308
PropertyAndCasualtySubsidiaries [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	40,498	38,734
Statutory net income	8,123	6,903	$ 2,712
LifeSubsidiaries [Member] [Member]
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	1,507	1,225
Statutory net income	$ 74	$ 55	$ (148)