Fair value measurements Fair Value Measurements (Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Guaranteed Minimum Income Benefit
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	$ 559	[1],[2]	$ 609	[2],[3]	$ 406	[3]
Transfers Into Level 3, liabilities	9	[1]	0	[2]	0	[3]
Transfers out of Level 3, liabilities			0	[2]	0	[3]
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0	[1]	0	[2]
Net Realized Gains/Losses, Liabilities	(364)	[1]	(50)	[2]	203	[3]
Purchased, liabilities	0	[1]	0	[2]	0	[3]
Sales, liabilities	0	[1]	0	[2]	0	[3]
Settlements, liabilities	0	[1]	0	[2]		[3]
Balance - End of year, liabilities	204	[1]	559	[1],[2]	609	[2],[3]
GLB liability	550		853		888		$ 663
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	(364)	[1]	(50)	[2]	203	[3]
Other Derivative Instruments Fair Value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - Beginning of year, liabilities	13		6		4
Transfers Into Level 3, liabilities	0		0		0
Transfers out of Level 3, liabilities	(9)
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	(2)		5		2
Purchased, liabilities	0		2		0
Sales, liabilities	0		0
Settlements, liabilities	0
Balance - End of year, liabilities	2		13		6
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Liabilities	$ (2)		$ 5		$ 2

[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. Refer to Note 5 c) for additional information.

[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 $853 million at December 31, 2016 and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $559 million and $609 million, respectively.

[3] 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 $888 million at December 31, 2015 and $663 million at December 31, 2014, which includes a fair value derivative adjustment of $609 million and $406 million, respectively.