Fair value measurements Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - Guaranteed Minimum Income Benefit [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020		Mar. 31, 2019		Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Guaranteed Benefit Liability, Net	$ 1,591		$ 741		$ 897	$ 861
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	456		452
Balance - End of Period, Liabilities	1,141		338
Guarantees [Member] | Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	456	[1]	452	[2]
Transfers into level 3, liability	0		0
Transfers out of Level 3, Liabilities	0		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	685		(114)
Purchases, Liabilities	0		0
Sales, Liabilities	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0		0
Balance - End of Period, Liabilities	1,141	[1]	338	[2]
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss)	$ 685		$ (114)

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $1,591 million at March 31, 2020, and $897 million at December 31, 2019, which includes a fair value derivative adjustment of $1,141 million and $456 million, respectivel

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $741 million at March 31, 2019, and $861 million at December 31, 2018, which includes a fair value derivative adjustment of $338 million and $452 million, respectively