Investments (Collectively Significant Equity Method Investments - Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Carrying value of investments accounted for under the equity method	$ 2,400			$ 89
Unfunded commitments for investments accounted for under the equity method	$ 1,500
Percentage net investment income from investments in limited partnerships and LLCs exceeds consolidated pre-tax income (loss)	10.00%
Total assets for investments accounted for under the equity method	$ 403,600	$ 344,600
Total liabilities for investments accounted for under the equity method	52,700	30,100
Net income (loss) for investments accounted for under the equity method	$ 33,300	$ 33,300	$ 36,200