Investments - Unrealized Capital Losses 1 (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) securities	Dec. 31, 2018 USD ($) securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Available For Sale Securities Change in Loss Position	$ 450
More than twelve months below amortized cost, Number of Securities | securities	404,000,000	550,000,000
Total Unrealized Capital Losses	$ 110	$ 560
Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
More than twelve months below amortized cost, Number of Securities | securities	6
Total Unrealized Capital Losses	$ 28