Supplemental Cash Flow Information - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Non-cash modifications of certain mortgage loans, fixed income securities, limited partnership interests and other investments, as well as mergers completed with equity securities	$ 106	$ 326	$ 131
Liabilities assumed	90	34
Non-cash financing activities related to the issuance of shares for vested restricted stock units	43	41	74
Liabilities for collateral received reported in other liabilities and accrued expenses	1,120	1,120	829
Obligations to return cash collateral for over-the-counter (OTC) and cleared derivatives reported in other liabilities and accrued expenses or other investments	$ 3	5	$ 11
Limited Partnership
Debt Instrument [Line Items]
Liabilities assumed		$ 89