Financial Instruments: (Details 4) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivative instruments in fair value hedging relationships | Interest rate swaps
Derivative Instruments, Gain (Loss)
Notional amount	$ 4,200,000,000	$ 4,300,000,000
Average remaining maturity	4 years 9 months 18 days	5 years 1 month 6 days
Derivative instruments in cash flow hedging relationships | Foreign exchange forward contracts
Derivative Instruments, Gain (Loss)
Notional amount	10,800,000,000	10,700,000,000
Average remaining maturity	8 months 12 days	8 months 12 days
Net gains (losses) in other comprehensive income in connection with cash flow hedges	166,000,000	(138,000,000)
Gains (losses) expected to be reclassified to net income within the next 12 months	200,000,000	(79,000,000)
Maximum length of time hedged	4 years
Derivative instruments in cash flow hedging relationships | Interest rate swaps
Derivative Instruments, Gain (Loss)
Net gains (losses) in other comprehensive income/(loss), cash flow hedges of borrowings	1,000,000	1,000,000
Gains (losses) expected to be reclassified to net income within the next 12 months	1,000,000	1,000,000
Derivative instruments in net investment hedging relationships
Derivative Instruments, Gain (Loss)
Notional amount	3,500,000,000	3,300,000,000
Average remaining maturity	2 months 12 days	4 months 24 days
Derivative instruments not designated as hedging instruments | Foreign exchange forward and swap contracts
Derivative Instruments, Gain (Loss)
Notional amount	15,400,000,000	12,900,000,000
Maximum length of time hedged	1 year
Derivative instruments not designated as hedging instruments | Equity contracts
Derivative Instruments, Gain (Loss)
Notional amount	$ 1,200,000,000	$ 1,200,000,000