Investments (Collectively Significant Equity Method Investments - Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss)
Carrying Value of investments accounted for under the equity method			$ 13,800
Unfunded commitments for investments accounted for under the equity method			4,800
Total assets for investments accounted for under the equity method			505,600	$ 436,900
Total liabilities for investments accounted for under the equity method			68,900	56,400
Net Income (loss) for investments accounted for under the equity method			$ 37,900	26,800	$ 25,800
Aggregate Net income Exceeded Stated Percentage Of The Pre Tax Income (Loss) From Continuing Operations	10.00%		10.00%
Brighthouse Financial, Inc [Member]
Equity Method Investment, Summarized Financial Information, Gross Profit (Loss)
Total assets for investments accounted for under the equity method				9,600
Total liabilities for investments accounted for under the equity method				177
Net Income (loss) for investments accounted for under the equity method		$ 1,100		$ 270