Employee Benefit Arrangements - Fair Value of Plan Assets (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) fund_asset	Dec. 31, 2018 USD ($) fund_asset	Dec. 31, 2017 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 1,964,000,000
Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		$ 0
U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		0
U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		0
Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		0
Other fixed maturities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		0
Small/Mid-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, net asset value		0
Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	4,000,000
Net, total pension assets, net asset value	0
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	226,000,000
Level 1 | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	4,000,000
Net, total pension assets, net asset value	4,000,000
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,205,000,000
Level 2 | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0
Net, total pension assets, net asset value	0
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000
Level 3 | Other fixed maturities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Level 3 | Derivatives
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0
Net, total pension assets, net asset value	0
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,960,000,000	1,605,000,000	$ 1,764,000,000
Net, total pension assets, net asset value	519,000,000	432,000,000
Pension Plan | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,070,000,000	752,000,000
Net, total pension assets, net asset value	98,000,000	48,000,000
Pension Plan | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000	0
Pension Plan | Short-term investments fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	98,000,000	48,000,000
Net, total pension assets, net asset value	98,000,000	48,000,000
Pension Plan | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	97,000,000	131,000,000
Pension Plan | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	796,000,000	506,000,000
Pension Plan | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	64,000,000	66,000,000
Pension Plan | Other fixed maturities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,000,000	1,000,000
Pension Plan | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	733,000,000	684,000,000
Net, total pension assets, net asset value	260,000,000	217,000,000
Pension Plan | Large-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	358,000,000	369,000,000
Net, total pension assets, net asset value		0
Pension Plan | Small/Mid-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	115,000,000	98,000,000
Pension Plan | International Commingled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	235,000,000	188,000,000
Net, total pension assets, net asset value	$ 235,000,000	$ 188,000,000
Number of assets In fund | fund_asset	2	2
Pension Plan | International Commingled Funds | Baillie Gifford Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 125,000,000	$ 94,000,000
Unfunded commitments	0	0
Pension Plan | International Commingled Funds | Silchester
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 110,000,000	$ 94,000,000
Number of business days prior to month-end clients must submit redemption request	6 days	6 days
Unfunded commitments	$ 0	$ 0
Pension Plan | Equity Securities, Limited Partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of assets In fund | fund_asset	2	2
Pension Plan | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 25,000,000	$ 29,000,000
Net, total pension assets, net asset value	25,000,000	29,000,000
Pension Plan | Pantheon Europe | Pantheon Europe
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	3,000,000	4,000,000
Unfunded commitments	1,000,000	1,000,000
Pension Plan | Pantheon USA | Pantheon USA
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	22,000,000	25,000,000
Unfunded commitments	5,000,000	5,000,000
Pension Plan | Other investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	161,000,000	169,000,000
Net, total pension assets, net asset value	161,000,000	167,000,000
Pension Plan | Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	80,000,000	92,000,000
Net, total pension assets, net asset value	80,000,000	92,000,000
Pension Plan | Real estate | UBS Trumbull Property Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 80,000,000	$ 92,000,000
Number of business days prior to month-end clients must submit redemption request	60 days	60 days
Real return performance objective, rate of return	5.00%	5.00%
Pension Plan | Real estate | UBS Trumbull Property Fund | Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Real return performance objective, rate of return, determination period	3 years	3 years
Pension Plan | Real estate | UBS Trumbull Property Fund | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Real return performance objective, rate of return, determination period	5 years	5 years
Pension Plan | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 81,000,000	$ 75,000,000
Net, total pension assets, net asset value	81,000,000	75,000,000
Pension Plan | Limited partnerships | Magnitude Institutional, Ltd.
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	81,000,000	75,000,000
Pension Plan | Other derivatives, net
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value		2,000,000
Net, total pension assets, net asset value		0
Pension Plan | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	222,000,000	601,000,000
Pension Plan | Level 1 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	111,000,000	132,000,000
Pension Plan | Level 1 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000	0
Pension Plan | Level 1 | Short-term investments fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	97,000,000	131,000,000
Pension Plan | Level 1 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	1,000,000
Pension Plan | Level 1 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Other fixed maturities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	115,000,000	467,000,000
Pension Plan | Level 1 | Large-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	369,000,000
Pension Plan | Level 1 | Small/Mid-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	115,000,000	98,000,000
Pension Plan | Level 1 | International Commingled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Other investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	2,000,000
Pension Plan | Level 1 | Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 1 | Other derivatives, net
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value		2,000,000
Pension Plan | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,205,000,000	565,000,000
Pension Plan | Level 2 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	847,000,000	565,000,000
Pension Plan | Level 2 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Short-term investments fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	782,000,000	498,000,000
Pension Plan | Level 2 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	64,000,000	66,000,000
Pension Plan | Level 2 | Other fixed maturities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	1,000,000	1,000,000
Pension Plan | Level 2 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	358,000,000	0
Pension Plan | Level 2 | Large-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	358,000,000	0
Pension Plan | Level 2 | Small/Mid-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | International Commingled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Other investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 2 | Other derivatives, net
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value		0
Pension Plan | Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000	7,000,000
Pension Plan | Level 3 | Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000	7,000,000
Pension Plan | Level 3 | Cash and cash equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Short-term investments fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | U.S. Government securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | U.S. corporate, state and municipalities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	14,000,000	7,000,000
Pension Plan | Level 3 | Foreign securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Large-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Small/Mid-cap domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | International Commingled Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Other investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Real estate
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	0	0
Pension Plan | Level 3 | Limited partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value	$ 0	0
Pension Plan | Level 3 | Other derivatives, net
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net, total pension assets, fair value		$ 0