Shareholders' Equity - Adjustments to Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Interest-rate contracts	$ 510	$ 512
Sales of non-U.S. entities, net of related taxes of $0 and $0, respectively	91	306
Total reclassifications into AOCI	(18)	4
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gains (Losses) on Available-for-Sale Securities
Class of Stock [Line Items]
Net realized gains (losses) from sales of available-for-sale securities, net of related taxes of $16 and ($1), respectively	(24)	3
Net realized gains from sales of available-for-sale securities, taxes	16	(1)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Actuarial Losses
Class of Stock [Line Items]
Amortization of actuarial losses, net of related taxes of ($3) and ($2), respectively	6	1
Amortization of actuarial losses, taxes	$ (3)	$ (2)